Gemstone Mining Methods

by Sheweta Dhanuka

Gemstones are treasured by most of us and to retrieve these precious gems from deep down the earth crust one has to go in for treasure hunt. Gemstone Mining is very complex and tedious process that requires huge input of valuable resources such as time, workforce, equipments and knowledge etc. There are different methods for recovering the gemstone from the lap of Mother Nature. The appropriate procedure is selected depending upon the circumstances but no matter what method is selected the entire process of gemstone mining needs to be very systematic as it costs a lot of money. The total process of gemstone mining is so intricate that inspite of putting in so much efforts there is no surety of the results. Failures and disappointments always have higher percentage than the success.

In order to attain the positive results, the first and foremost requirement of this exclusive process is to identify the gemstone deposits. This necessitates the vast knowledge of gemstone properties, with the help of this key the deposits are identified where there could be the probability of the finding the precious and semi precious gems. The route of gemstone mining is executed all the way through highly developed and technical system. But we all know, traditional methods have there own uniqueness that cannot be denied even after developing new scientific methods. All the methods are categorized into two types of mining viz. surface mining and underground mining. First always the surface mining is done and then when fruitful results are not achieved underground mining is brought into action. Underground mining is always more expensive because –

• It takes long working hours.
• For underground mining more advanced equipments are required.
• There are extra costs incurred for activities such as pumping, electricity, digging etc.

Surface Mining

Surface Mining is done to obtain gemstones from the rocks near to the surface of the land. There are six different types in which surface mining could be done. The miner decides on surface mining technique depending up the overall cost and time. These methods are:

[1] Hydraulic Mining

In this method powerful jets of water is used to loosen the gem material from the overburden. The miners make channels on the rock/gravel hillsides in form of sluices where water under pressure is sprayed. The water pressure splits down the rock and washes large rock piece of it downhill. And finally the gems as raw stones are separated. This mining is very harmful for the environment as it wrecks the mountains and blocks the rivers. Hydraulic surface mining was found way back in 1800s and continued till 1960s but now it is stopped completely due to its disastrous consequences to the natural beauty.

[2] River Panning

River Panning is the method where gemstones are collected while washing the gravels from a river/stream in the mining area. It is also known as placer mining. This method is initiated with the identification of the gravel which may contain gems. The best place to find the gravel deposits is in obvious gemstone producing rivers, streams and creeks. Then a large pan is filled with water and shaking it back and forth to settle the heavy material to the bottom of the pan. The lighter material is washed over the top of the pan and larger rocks & pebbles are removed by scooping them over the edge. These steps are repeated until there is only about a tablespoon or two of concentrates left in the pan. Nearly all panning is completed using the riffles in the pan.

The left over concentrated is then shifted to a smaller clean pan. Drop of liquid soap is added to keep the tiny chips from “floating.” The less weighty material shall float down with the water and the gems, in case the gems are there, it shall stick and stay at the upper end of the pan. This is a very time consuming method and the chances of success are very less.

[3] Open Pit Mining

This mining can only be accomplished under the guidance of an experienced Gemologist. First he scrutinizes the location to be mined with respect to value of the rock and minerals below the surface, cost of digging the mine and the after effects of mining on the environment. The monetary value of rocks and minerals keeps appreciating over the years so once it is profitable to mine then only open pit mining is done.

Once the location is finalized, layers of the land are removed one after the other till rocks are visible. Then the rocks are removed and gems are searched for in the rocks and sent for further processing. Sometimes explosives like dynamite are used to reach deeper and deeper to recover the required rock possessing the gems. After the mining is done, the area turns into pit which is used as landfill. Landfill is huge open space used for dumping the garbage. Once it is fill it is covered the layer of mud. Finally when the trash decomposes in long run and land can be again used for some other purpose apart from mining. This mining method is relatively easy and cost effective. However, it is performed only when rocks are near to the surface of the land.

[4] Strip Mining

This process is very similar to open pit mining. The mining site is identified; the trees and bushes are removed with the help of the bulldozer. The remains are dumped at the nearby area. Many small-small holes are drilled distant from one another through the rock. Dynamite are placed inside these holes and blasted to get the rocks with gemstones. Raw stones then are sent for further processing. This mining is done in long strips so it is called as strip mining. Once the first strip is completed, the second strip starts. The dirt obtained in making the second strip is dumped in the first strip. Similarly it goes on till the entire site is worked on. And in the last strip the remains of the first strip is filled in. The top layer is of mud that is leveled on all the strips together making the land ready of re-use.

[5] Mountaintop Removal Mining

In this mining method, the mountain top at the ground level is cleaned by cutting the trees and shrubs. Then using the dynamite the top of the mountain is blasted for making the vein. This gives huge blocks of rocks from which the gemstone in unprocessed form are retrieved. The dirt obtained after the blast is dumped into the valleys with the help of bull dozers and trucks.

[6] Quarrying

This mining method is quite less hazardous to the environment. The rock attained from this mining is used for making buildings. Therefore, the way quarrying is to be done depends upon the purpose of re-use of rock. The rocks are drilled to use the left over for cement, it is blasted with dynamite to use the rocks for the interiors of the house like flooring, kitchen slabs. In any of the method after getting the rock the gemstones are searched and then the rocks are spared for re-use.

Underground Mining

Underground mining is done when surface mining is not possible or does not yield rewarding results. Moreover, precious gemstones are mostly found through underground mining. In the method the miners make underground rooms where they further dig the ground more and deeper. Underground mining is done in numerous ways. These are –

[1] Borehole Mining

As the name suggests holes are drilled very deep inside the plain land. In these holes a long huge tube (having enough space to allow the water to pass through) is dropped. Then water is pushed down the tubes with the force, the water hits the rock and breaks it down. The water combines with the rocks, dirt and mud to make slurry. This mixture is pumped back from the tubes and stored into tanks. The unwanted water is thrown out the left over rocks are processed for gems. This method is very much environment friendly and the shifting from one place to another is quite easy.

[2] Drift Mining

This mining is done on the mountain sides. Rock are identified which are on the sides of the mountain. The opening is made below the identified rock. These opening are made horizontally and are known as tunnels/drifts. From the drifts the desired materials are retrieved as due to gravity the material comes down the hill easily. This is one of the cheapest gemstone mining methods and gives good results as well.

[3] Shaft Mining

In this method, vertical tunnels are created below the mountains and through the lift miners moves up and down the mines. The vertical tunnels are called as shafts. Two shafts are created. One is used for the movement of the miners inside the shafts and the other shaft for brining the material on the ground. From the man shaft, small tunnels are made that reaches the rocks possessing the gems. These small tunnels are used for blasting and when the rocks breaks into small chunks those are brought up on the ground through the second shaft. After the work is finished the mines are closed by refilling the shafts with dirt, mud, pebbles and cement etc. This is quite a costly method.

[4] Slope Mining

Slope mining too has shafts but these shafts are first made slant and then parallel to the ground. Usually, this mining is done when it is not possible to make the straight shafts therefore it is named as slope mining. The tunnels are not very deep in the gemstone mining method. Using the conveyor the broken are rocks are brought out.

[5] Hard Rock Mining

Same as drift mining, tunnels are made inside the grounds instead of mountains. First a small opening is made which is referred as Adit. Later, using Adit, tunnels are made vertically deep down the ground using explosives like dynamite. The tunnels are called as shafts. Like wise many shafts are made and each one has a different function. For examples – one could be used for miners going inside and coming back to the ground, second for air ventilation and so on. At the end of the shaft, there one more shaft is made that leads to the rock that contains gemstones. Deep inside the earth crust many different floors are created and one floor after the other is completed. This is the most dangerous gemstone mining method and therefore is brought into practice quite less.

In all the mining methods the rocks are broken into medium or small chunks using the explosives such as dynamite. The broken rocks are then sent to the other processing plant where the gemstones are obtained in the form of raw stone. These raw stone reach to the next level of gemstone processing that involves cleaning, cutting and polishing etc. The gemstone that finally gets mounted to the awesome jewelry pieces, from the scratch passes through the numerous steps that involve the sweat of many people.

It is very easy and classy to wear the gemstone jewelry but the amount of hard work involved in obtaining these precious and semi-precious gemstones through the mining methods is immense. Gemstone mining methods are certainly mind-numbing and it is an exclusive proficiency of finding inimitable raw stones from mines that are crafted into amazing gemstone jewelry!!

Diamond Marketing by De Beers

by Erum Qureshi

That ‘a diamond is forever’ is the probably the world’s greatest, most expensive and widely circulated PR scam! The on-going, century-long campaign by diamond giant De Beers owned by the Oppenheimer family began in 1938; De Beers needed a slogan for diamonds that expressed both the theme of romance and everlasting love.

The on-going, century-long campaign by diamond giant De Beers owned by the Oppenheimer family began in 1938; De Beers needed a slogan for diamonds that expressed both the theme of romance and everlasting love.

Consequently, N.W Ayer, De Beers’ New York based ad agency, came up with the line ‘A diamond is forever’. Even though diamonds can be shattered, chipped, discolored or reduced to ash, the concept of eternity perfectly captured the magical qualities their client wanted to attribute to their product. The campaign began in America and projected the diamond onto the man-woman relationship, subtly altering the public’s view of the way a man courts, and wins a woman. That it was forever also aimed to associate the stone with a sentiment that inhibited the public from ever reselling it. Ask anyone who has tried reselling their diamonds, and they will tell you how it is practically impossible to even recover a diamond’s cost price, let alone make a profit on that investment.

De Beers controls over 60% of the world’s diamond market; it has stockpiles of the stones and sets the price on them. However, this invention was more than just a monopoly for fixing diamond prices, it was a strategy formulated for De Beers by N.W Ayer in America and later followed by J. Walter Thompson in the rest of the world for converting carbon crystals into globally accepted icons of wealth, romance and power.

The diamond ring was pitched not as a marketable product but as a symbol of everlasting love and security and an inseparable part of courtship and marital bliss. There was no direct sale to be made, no brand name to be impressed on the public, just the idea of eternal emotional value surrounding the diamond. The pitch succeeded. And how! Except for those few stones that have been destroyed, every gem quality diamond that has ever been cut and polished still exists today.

Kimberly diamond mine, owned by De Beers group

Nearly a hundred million women wear diamonds, while millions of others keep them in vaults and safe-deposit boxes as family heirlooms. The public holds an estimated 500 million carats of gem quality diamonds (more than fifty times the annual production of gem quality diamonds in any given year by De Beers). If a significant section of the public ever decided to put these diamonds up for sale in the market, the price so carefully controlled and sustained by De Beers could never be maintained. For the diamond invention to survive, for De Beers itself to survive, these hundred million women had to be stopped from ever parting with their diamonds.

It was the symbolism, not the value. The idea that diamonds are a gift of love: the larger and finer the diamond, the greater the expression of love. Men are aware of the symbolism value, which is why they have to buy a diamond ring even if they know it’s a creation of the De Beers monopoly. De Beers spent millions to ingrain in the minds of everyone that they have to shell out thousands for the diamond if a man wants to marry his woman. It was how one could make ‘two months’ salary last forever’!

De Beers sent representatives to high schools across the country to teach young girls about the value of diamonds and feed them romantic dreams. Word was spread by diamonds worn by Hollywood stars, British Royalty and wives and daughters of political leaders and celebrities, by women who could make the common man’s wife or girlfriend say ‘I wish I had what she has’. Love began to be measured in carats.

In the 1960’s diamonds were discovered in Siberia and De Beers saw its control-supply chain monopoly being threatened. It closed a secret deal with the Soviets to market these small stones and the marketing campaign for ‘eternity anniversary rings’ was launched, targeting an entirely new market of older married women.

Perhaps the biggest controversy De Beers ever faced was that of Conflict Diamonds. Although the industry has started following the Kimberly process (wherein a diamond is monitored and certified at every point of its production process), not very long ago De Beers was still buying Angolan diamonds and insisting that tracking stones was unfeasible. No ad campaign for De Beers ever highlighted the fact that mining undertaken in African countries violate innumerable human rights. In these mines, small children are made to dig in small underground pits, where men and women can’t fit, even though child labor is illegal.

Workers and communities in and around mines suffer due to state orchestrated repression, toxic run-off from unsafe mining practices, tuberculosis, HIV infections, prostitution, immune disorders, racial discrimination and slavery. In the past decade, millions of people have been dispossessed of their livelihoods, land, future and their lives in places like Katanga, Congo and Zaire where De Beers has its mining operations. Such topics are off the agenda for De Beers, the media and the women who choose to wear these diamonds. For them, it serves to 1) Reassure them that a man values them,
2) Reassures them that he is financially stable, and
3) Draws respect from other women because of Nos. 1 and 2.

The question why the people from the world’s richest mining metropolises are also one of the world’s poorest and most downtrodden does not occur to anyone.

Back home in India where 80 % of the world’s diamonds are cut, children are given the smallest stones to work on because their eyes and fingers are better suited for shaping the tiny facets. These children suffer from eyestrain, repetitive motion injuries and lacerated lungs from diamond dust. Skilled laborers in India earn less than 1/5th of what their counterparts in Europe or America do. Where is the romance in that?

Today, being faced with increased competition, the threat of synthetic diamonds and newly discovered diamond reserves, De Beers has decided to stop buying the world’s surplus diamonds as it has been doing all these decades to control supply. It markets itself as a clean diamond company, guaranteeing bloodless stones because it lies in its best commercial interests to do so. It would even suit De Beers if the supply of African diamonds somehow dried up; they could then get rid of its $4bn stockpile of accumulated carbon. As always, exploiters minimize the awareness of the resources they target, laying emphasis instead on the glamour and lure of the product they market.

Differentiating Diamond and its Imitation

by Erum Qureshi

There are various decisive tests to assess the authenticity of a diamond. The Ceres Diamond probe, Rayner Diamond Tester, Diamond Pen are a few popular instruments.

The unique hardness of diamond enables it to scratch the polished surface of synthetic corundum and no other substance on earth can do this. However, using hardness as a test is considered crude and seldom necessary since the diamond itself may suffer some damage in doing so.

The most notable diamond Simulants are synthetic cubic zirconia, synthetic strontium titanate, YAG (yttrium aluminium garnet) and GGG (gadolinium gallium garnet).

Synthetic white spinel, made from the Verneuil flame-fusion process is also used as a substitute for small diamonds in multiple gem settings; moreover, it is singly refractive. But it gives a Refractometer reading of 1.726, has a low degree of fire, and measures 8 on Moh’s scale of hardness. Synthetic rutile has six times the dispersion of diamond but is easily recognizable because of its high refractive indices and a large double refraction. YAG (yttrium Aluminium garnet) has the appearance of having properties of a diamond Simulants, and is differentiated from diamond by the Immersion Contrast method.

Danger of confusion between diamond and its simulants became much more apparent when Cubic Zirconia appeared on the market.

There was a demand for developing special apparatus that would make the distinction between diamond and its Simulants rapid and certain, even in the case of mounted stones and with a very rudimentary knowledge of gemology. The most ingenious and effective method of differentiating diamond from all other gemstones makes use of its outstanding property as a thermal conductor, which is higher than for any other substance – higher than even copper or silver.

The Ceres Diamond probe was the first to exploit this property even with small specimens and in the case of mounted stones. The Ceres probe has two thermistors and a small copper tip in a convenient holder. When the instrument is switched on, the tip of the probe warms up. When it is gently held to the surface of the stone to be tested, the needle of the instrument swings to the right and a green light flashes in case of a diamond. With any other stone, the needle of the meter swings to the left and a red light flashes. The probe of the Ceres instrument is very delicate and needs handling with care, but even very small stones can be tested with it.

Another instrument of the same kind is the British made Rayner Diamond Tester. Such equipment is very costly but to anyone dealing with diamond jewelry, this is a relatively small matter when compared with the value of the goods tested.

The GIA has made use of another property of diamond to differentiate it from simulants. This particular property is the diamond’s affinity for grease or greasy liquids. The Gemological Institute of America has produced a Diamond Pen, charged with a specially prepared liquid, which left a visible mark when drawn across the table facet of a diamond, but which broke up into droplets on the surface of all other stones.

Another test for singling out a diamond simulant is the Immersion Contrast method. When light is placed over stones (Strontium titanate, YAG, GGG and CZ) immersed in di-iodomethane (methylene iodide; a high density liquid with a refractive index of 1.742) or Refractometer contact fluid (RI 1.81) different stones show differing patterns. All except strontium titanate show a dark ring diminishing in width as their refractive index approaches near to that of the liquid. This is a definite visual indication of differentiation between diamond and its simulant.

Another diamond simulant, though very rare, is a diamond doublet. The top half (crown) of this consists of a diamond, which is cemented on to a pavilion of some other colorless stone. When such a stone is viewed obliquely through the table facet, a shadow of the edges of the facet can be seen on the underlying cement layer, revealing the fake.

Another way to differentiate between a diamond and its simulant is ultra violet radiation. Under long-wave ultra-violet light, diamonds will show a very varied degree of fluorescence. If all the ‘diamonds’ in a multi-stone setting show a similar fluorescence, they are certainly not diamonds. Under X-rays, almost all diamonds show a blue fluorescence and a brief exposure on film will show diamonds to be far more transparent to X-rays than any other stone. This technique is worth practicing as it is a decisive test.

Fake Gemstone names

by Mark

List of Fake and false gemstone names and its Preferred Gemological Names.

World Famous Gemstones

by Mark

Stunning gallery of few world famous gemstones pictures, Just flip through the images to see the next one.

The Guinness Emerald Crystal

The 1759-carat Guinness Emerald Crystal. The stone was found at the Coscuez in Columbia and is one of the largest gem-quality emerald crystals in the world

The Logan Sapphire Brooch

422.99-carat Logan Sapphire from Sri Lanka. It is the heaviest mounted gem in the National Gem Collection, and is framed in a brooch setting surrounded by twenty round brilliant-cut diamonds, totalling 16 carats.

The Mackay Emerald Necklace

The largest cut emerald in the National Gem Collection designed by Cartier Inc. In 1931, Clarence H. Mackay presented the necklace as a wedding gift to his wife, Anna Case

The Mandalay Ruby

Origin unknown, Mandalay Ruby is one of the largest fine rubies in the world

The Maria Alexandrovna Sapphire Brooch

260.37 carats, Russian Emperor Alexander II presented this to his wife, Empress Maria Alexandrovna.

Lindsay Uncut Topaz

On the left side The Lindsay Uncut Topaz, weighing 70 lbs, right side: The Freeman Uncut Topaz, weighng 111 lbs. Center: The American Golden Topaz

The American Golden Topaz

Weight: 22,892.50 carats, largest cut yellow topaz in the world, and one of the largest faceted gems in the world.

The Bismark Sapphire Necklace

98.6-carat deep blue sapphire in a diamond and platinum necklace.

The Chalk Emerald Ring

37.82-carat Chalk Emerald ranks amoung the very finest Columbian emeralds, it was once the centerpiece of an emerald and diamond necklace belonging to a maharani of the former state of Baroda in India.

The Delong Star Ruby

The Delong Star Ruby resides in the Natural History Museum in New York City. It weighs 100.32 carats.

The Gordon Sapphire Necklace

This piece belonged to Aron Gordon, the founder of Gordon Jewelers. Here is what Sotheby’s had to say about the piece: “The pendant set with an emerald-cut sapphire weighing approximately 50.00 carats, within a clustered frame set with 10 marquise-shaped, 26 pear-shaped, 7 round and 25 baguette diamonds weighing approximately 14.50 carats, the necklace set with 51 round, 56 marquise-shaped and 4 pear-shaped diamonds weighing a total of approximately 22.50 carats, mounted in platinum, length 17 inches, pendant detaches, may be worn separately as a brooch. Estimate: $50,000 to $70,000.

The Gordon Star Sapphire

52.00 carats, framed by 24 pear-shaped diamonds weighing approximately 6.60 carats, mounted in platinum, ring shank detachable, retractable pendant loop.

The Midnight Star Ruby

116.75-carat deep purplish-red star ruby is part of the New York Museum of Natural History’s collection.

The Mogok Ruby

Alan Caplan Ruby or the Mogok Ruby is 15.97-carat untreated Burmese stone, Sultan of Brunei gifted this as an engagement ring for one of his wives.

The Patricia Emerald Crystal

It is one of the largest gem-quality emeralds in the world, The stone resides in the New York Museum of Natural History.

Queen Marie of Romania’s Sapphire

A cushion-shaped sapphire weighing 478.68 carats, King Ferdinand of Romania purchased this for Queen Marie.

The Ruspoli Sapphire Crystal

133.06 carats sapphire, Paris Museum of Natural History.

The Star of Bombay

The 182-carat Star of Bombay sapphire is from Sri Lanka. It was given to silent film star Mary Pickford by her husband, Douglas Fairbanks Sr, currently at Smithsonian Institute.

The Stuart Sapphire

The stone was set in Queen Victoria’s State Crown, on the front just below the Black Prince’s Ruby

Hooker Emerald Brooch

A 75.47-carat emerald set in a brooch, part of the Smithsonian Museum’s collection.

Black opal ring

422.99-carat Logan Sapphire from Sri Lanka. It is the heaviest mounted gem in the National Gem Collection, and is framed in a brooch setting surrounded by twenty round brilliant-cut diamonds, totalling 16 carats.

Star of Asia

329.7 carats star sapphire, and it’s part of the Smithsonian Museum’s collection.

Opal Peacock Brooch

This brooch is part of the Smithsonian Museum’s collection, and it was donated by Harry Winston Inc.

Maximillian Emerald Ring

Donated to the Smithsonian Museum by Marjorie Merriweather Post.

Basic Crystallography

by Ritika

Basic crystallography is about the fundamental principles of geometrical crystallography which are brought in through the medium of symmetry operations, lattices, and the creation of point and space groups.

The study of mineralogy has a fascinating division – Crystallography. One can’t help admiring crystals like pyrite, quartz, or tourmaline which are esthetically pleasing. Crystallography basically means the study of crystals. Crystals refer to all minerals with well-expressed crystal shapes. Crystallographers have been able to get important information about the type and the various stages of formation of crystals through analysis and thus crystallography has become an important branch of science.

Crystallography is divided into 3 sections – geometrical, physical and chemical. Crystal is a standard polyhedral form bound by smooth faces made of chemical compound which forms into a crystal due to the action of inter-atomic forces under specific conditions. Nicholas Steno, a Danish scientist found that irrespective of the conditions in which the crystal grew, the angle of the crystal remains the same. It has been recently proved that this is because of the geometric relationships which retain the structure.

We also find crystals which are not symmetrical in their angles which are quite common and this condition is because of the breakage of minerals. Crystallography proves how during the formation of crystals they get different geometric shapes due to the atomic structure and the conditions under which they form. All crystal forms fit into six crystal systems – Cubic, Tetragonal, Orthorhombic, Hexagonal, Monoclinic, and Triclinic. Most crystals have a center of symmetry even if they don’t have planes of symmetry or axes of symmetry.

Basic crystallography is all about the fundamental principles of geometrical crystallography which are brought in through the medium of symmetry operations, lattices, and the creation of point and space groups. X-ray crystallography shows how spot intensities are bound by the unit cell and various diffraction directions rely on the lattice.

Basic crystallography studies the distribution of atoms in all forms of matter like liquid, gas and any other form.

The different shapes of crystals

• Acicular crystals which are thin needle-like.
• Botryoidal which look like a bunch of grapes
• Crystal Face is one of the flat surfaces of the crystal
• Form which is the group of crystal faces which are alike
• Lamellar which looks like the thin leaves of the book
• Pinacoid which are the crystal faces which are parallel to crystal axes and cut across by the third axis
• First order where the prism is cut by two lateral axes
• Striations where the crystal face has lines.

Talking about the Basic Crystallography Kit used by students, the kit is an efficient screening method for finding out the solubility and starting conditions for the crystallization. The crystallographers investigate a variety of other materials like glasses, fibers, etc. The different methods used by them are: high and low temperature studies, neutron diffraction, high pressure diffraction, electron crystallography, micro gravity experiments, molecular modeling and atomic force microscopy. Crystallographers have recently discovered how proteins recognize the shape of DNA to turn genes on and off.

To have a career as a crystallographer, biology, chemistry, physics, and mathematics are important and any advanced sciences courses will be useful. English and writing skills are also important. At the graduate level, a crystallographer develops and refines a specialty and gains experience on this.

The IUCr is the union adhering to International Council for Science with objectives to promote international cooperation in crystallography, to promote publication of crystallographic research, standardization of methods, units and symbols and relations of crystallography to other sciences.

What is Crystallography

by Ritika

Crystals are known for their beautiful external appearance. However, it is their internal structure, which is too small to be seen by the naked eye, that makes them interesting to scientists. The study of the growth, shape, and geometric character of these beautiful forms of minerals is called crystallography.

Crystals are known for their beautiful external appearance. However, it is their internal structure, which is too small to be seen by the naked eye, that makes them interesting to scientists. The study of the growth, shape, and geometric character of these beautiful forms of minerals is called crystallography.

A crystal is matter which is homogeneous and has a specific and orderly atomic structure. The outward appearance of the crystal has plane and smooth surfaces which are arranged symmetrically. Whenever a solid is formed from a fluid, a crystal is formed. Crystals could be formed as of result of either a liquid being frozen, or dissolved matter being deposited or even a gas being directly converted into a solid state.

The angles that are formed between the corresponding sides of any 2 crystals of the similar matter are identical even if there are differences in size and external appearance. Almost all solid matter has an organized atomic arrangement and has a crystalline structure. Amorphous solids, like glass, are the solids that do not have a crystalline structure. Amorphous solids are more like liquids in structure.

Under the earths surface there are liquids that slowly freeze to form granite. These liquids sometimes flow out of volcanoes and cool down quickly. They thus form a rock that looks glassy and is known as obsidian. If this cooling is even a little slower, it forms a rock – felsite. Felsite is crystalline in nature but the crystals cannot be seen by the naked eye. It is also called cryptocrystalline or aphanitic. When the lava cools down even slower than this, it forms a porphyritic rock. The crystals are however, larger and can be seen easily. This rock called rhyolite may be identical in composition to obsidian rocks, felsite rocks or even granite.

Under favorable conditions some chemical elements and compounds also form crystals which are of a distinct and characteristic form. Salt, as an example of this, forms cubic crystals, while garnet which forms cubes too, sometimes is in the form of dodecahedrons (which has 12 faces) or trisoctahedrons (which has 24 faces). Though there may be differences in shape the crystallization of both salt and garnet is found to be of the same class and in the same system.

In theory, there are 32 classes under which crystals can be formed. Most minerals fall into the first twelve classes. Some of these classes are yet to be observed by scientists. These thirty-two classes can be classified into 6 different crystal systems. These systems are based on the length and position of the crystal axes, on the imaginary lines which are believed to be passing through the center of the crystal, on the intersection of each face, and having clear relations with the crystal symmetry. In each of these systems, the minerals share some details where the crystal forms are symmetric and several significant optical properties are common too.

The 6 crystal systems that are extremely focal to the study of mineralogists and gemologists are named and explained below. The specifications of the system are necessary in the explanation of any mineral.

Isometric

In this system all the crystals have three axes which are all perpendicular to one another and are all equal in length. An example of an Isometric crystal is pyrite which has three perpendicular axes of equal length. Of all the crystals this structure is the most symmetrical. Pyrite crystal system forms rocks that are hard and yet brittle. Pyrite is yellow in colour and has a metallic lusture which results in its being called ‘fool’s gold’.

Tetragonal

In this system all the crystals have three axes which are all perpendicular to each other and only two of these are equal in length. A fitting example of this is the Siberian idocrase which has three axes that are all perpendicular to one another and two are equal in length. Other rocks which Idocrase is grouped with are zircon, rutile, and wulfenite, which are not very hard rocks and at times possess a fire like a diamond.

Orthorhombic

In this system all the crystals have three axes which are mutually perpendicular and are all of different lengths. An example of this is Barite, from which barium is obtained. Barite has three axes that are mutually perpendicular and are of different lengths. Barite also exhibits a perfect cleavage, which means that it can split easily along specific planes that intersect.

Monoclinic

In this system all the crystals have three axes of which are not of equal lengths and two of them are not perpendicular to one another, but are both perpendiculars to the third axes. Gypsum is an example of this system. Gypsum is a soft, sedimentary rock from which plaster of Paris is obtained. It is also used in agriculture and construction.

Triclinic

In this system comprises all the crystals are with three axes which are not equal in length and are oblique to one another. Of all the crystal systems, crystals of this system are the least symmetrical. A good example is the Brazilian Axinite.

Hexagonal

In this system all the crystals have four axes. Of these, three axes are in a single plane; they are symmetrically spaced, and are of equal length. The fourth axes is perpendicular to the other three. According to some crystallographers this system can be split into two, thus forming a seventh system calling it the Trigonal or rhombohedral system.

The technique used to investigate the structure of matter in the crystalline state is called Crystallography. This technique studies the tri-dimensional arrangement of all matter; whether they are atoms, molecules or ions of minerals or molecules of life.

By using x-rays, in which crystals are subjected to an extremely energetic radiation, we can get information which allows a crystallographer to locate the specific entities that the crystals are made up of. There has been tremendous progress, in this field of science thanks to the introduction of automatization of the methods used and with computer development.

The results of these experiments and methods often explain the chemical, physical, biological and pharmaceutical properties of substance being analyzed. The most stimulating steps utilized in the study of crystallography today are aiding scientists in understanding the workings of life at the molecular level, which is leading medicinal practitioners in their discovery of new drugs to treat various diseases.

Physical Properties of Crystals

by Ritika

The physical properties of crystals like hardness, cleavage, optical properties, heat and electrical conductivity differ from crystal to crystal. Crystallographers deem it necessary to learn more about these properties so that they can determine what the crystals can be used for.

Crystallography is the scientific study of crystals where the arrangement of atoms and molecules in solid matter are determined. With the developments made in this field of science, crystallographers have found that crystals have numerous physical properties. It is important to know that all crystals do not possess the same properties and hence crystals have been classified into different classes and groups. Crystals have hence been divided into 32 different classes to make studying about them easier. Some of the important physical properties of crystals are discussed below.

Color

The color in crystals appears as some wavelengths of light are absorbed by the solid matter. Some metals like chrome and iron and some others have color as they are able to absorb these particular wavelengths of light. Color is not a very good property to use for identification of crystals as many different kinds of matter are of the same or similar color and can hence cause confusion.

Refraction of light

There is a change in the refraction of light through materials. The velocity at which light passes through a given material is inversely related to its index of refraction. For a vacuum, n = 1.0. It is found that in most of the minerals the range of the index of refraction is between 1.4 and 3.2.

Birefringence

This property is when there are two different refractive indices of light that are noticed, which cross-polarized when it enters matter. It is noticed that if one ray enters matter, there are two rays that emerge, these are called the ordinary and extraordinary rays. Should the material be rotated, the ordinary ray will remain still and the extraordinary ray makes a circle around the ordinary ray. This effect is easily seen in Calcite and Sodium Nitrate. The extraordinary rays which exit always display polarization at right angles.

Dispersion

This is the property when the refracted indices of light spread through a material in such a manner that it causes a variation in the wavelength from red to violet. When the dispersion of light in the material is larger, there is a greater amount of white light separated when the rays are exiting from the particular material. A good example is Diamond, where the dispersion of light is extremely great, hence one can see so many colors in this crystal.

Color Change

This property is of two types, One type of color change is Pleochroism in which the material seems to possess many different colors when it is looked at from different directions. When two colors are exhibited the effect is know as Dichroism. When three colors are exhibited the effect is called Trichorism. The mineral Iolite (cordierite) changes colors from dark blue to colorless, hence it is an example of dichroism.

The other type of change in color is noticed by the existence of artificial light, natural light, fluorescent light or even incandescent light. This type of change in color is noticed in nickel sulfate making it look like Alexandrite, which is a priceless gemstone.

Polarization of light

This property can be seen in some materials. This property is found naturally in tourmaline. As it is believed to be placed between what is called a “polarization sandwich,” sodium chlorate allows different colors through it, since there are changes in the angles between the polarizers.

Cleavage

This property refers to the ability of a crystal to break along certain specific planes with a lot more ease when compared with the other directions. Naturally crystals can break either perfectly or imperfectly. There is a marked difference between these two forms of cleavage. A perfect cleavage is one that will always break on the cleavage plane, which is found in fluorite, calcite and diamond. This property of the diamond makes cutting the gem very challenging as the planes the person is cutting along may not really be the cleavage planes. On the other hand imperfect cleavage is one in which it can break along any plane. Quartz and beryl are good examples. When quartz breaks, some of the broken pieces look very similar to glass.

Piezoelectric Effect

This is that physical property found in a compressed crystal, which causes a flow of charge and a drop in voltage across the opposite poles in the crystal. These materials are easily used in communication equipment. This effect is easily seen in both Rochelle salt as well as natural quartz, which are known to be able to supply voltage when mechanical force is applied. Materials like germanium, silicon, galena and silicon carbide are used as semi conductors as they carry current unequally in different directions.

Of the 32 classes of crystals 20 are piezoelectric. Crystals of the piezoelectric classes lack a center of symmetry. When an electric field is applied to any material it develops a dielectric polarization. Materials that naturally have a charge separation are called polar materials. The structure of the crystal determines whether it is polar or not. Of the 32 classes only 10 have polar crystals. Polar crystals are all pyroelectric and hence these ten classes are generally referred to as the pyroelectric classes.

Some crystal structures display ferroelectric behavior. Ferromagnetism, which is the similar to ferroelectric behavior, is a property where due to the electric field being absent, polarization is not displayed by the ferroelectric crystal. In the presence of an electric field the ferroelectric crystal displays permanent polarization. With the application of a large counter charge this polarization can be reversed just like it is reversed in a ferromagnetic. It is important to note here that though this effect is called ferroelectric, there is no presence of the ferrous metal and this effect is produced by the structure of the crystal.

The physical properties of crystals have been spelt out in detail in the above paragraphs. Crystallographers have made the study of crystals simple and convenient based on these properties.

Attributes of Crystals

by Ritika

The physical attributes of crystals need to be studied in detail for the categorization of crystals. This is a highly specialized field of crystallography.

There are various methods for categorizing a crystal. Generally the two common methods used for crystal categorization are:

• On the basis of crystalline structure
• On the basis of chemical or physical attributes

There are some main differences between facets and attributes of crystals in crystallography. Facets tell us about the actual classification system, i.e. the scheme and structure of crystals. But attributes of crystals in crystallography are simple values, not associated with a classification system. Also, attributes of crystals differ and are intrinsic to the nature of an object.

Crystal Groups Based on Lattices

On the basis of lattices or shape attributes of crystals, the crystals can be divided into seven crystal lattice systems. They are:

• Cubic which is also termed as Isometric: This include in it crystals of eight faces also termed octahedrons or crystals of 10 faces also termed dodecahedrons. Also, it is vital that cube faced crystals do not belong to this type of crystal lattice systems.
• Tetragonal: This has attributes same as cubic crystal lattice system with an additional attribute of being one axis longer. These form double pyramids and prisms shaped crystals.
• Orthorhombic: This has attributes similar to tetragonal crystals but do not have a square shape in cross section. These form rhombic prisms or dipyramids shaped crystals.
• Hexagonal: These include six-sided prisms with the cross section focusing a hexagon.
• Trigonal: This has single 3-fold axis of rotation.
• Triclinic: This crystal lattice system generally does not have normal shape. The reason for such shapes in this crsytal lattice system is because the crystal is not symmetrical from one side to the other.
• Monoclinic: One instance of the monoclinic crystal lattice system is skewed tetragonal crystals. These include prisms and double pyramids shaped crystals.

Crystal Groups Based on Physical and Chemical attributes

On the basis of physical and chemical attributes, crystals can be divided into four main categories. They are:

Covalent Crystals

Covalent crystals possess true covalent bonds with all atoms in the crystal thus focusing it as a big molecule. Another vital attribute possessed by crystal belonging to covalent crystals is that they have high melting points. Some crystals to name in the category of covalent crystals are diamond and zinc sulfide crystals.

Metallic Crystals

In the metallic crystals the outer electrons move freely around the lattice. This is because each metal atoms present in the metallic crystals lie on lattice sites. Another vital attribute possessed by crystal belonging to metallic crystals are they have high melting points and they are very dense.

Ionic Crystals

The ionic crystals possess ionic bonds and are bound together by electrostatic forces. One instance to name in the crystal to name in the category of ionic crystals is table salt. The vital attributes of ionic crystals are that they are hard and have high melting points.

Molecular Crystals

Molecular crystals possess non-covalent interactions also termed hydrogen bonding or van der Waals force. The main attribute of crystals belonging to molecular crystals are that they are soft and have low melting points. Some instances of molecular crystals category are rock candy which is nothing but the crystalline form of table sugar.

Let us study one example of crystal physical attribute of the diamond. Diamonds are high-pressure polymorphs of carbon and are meta stable at room temperature. Diamond focus lattice spacing of 1.54 and have closely packed carbon atoms. The hardness attribute of diamonds vary with the direction in the crystal, the hardest direction being normal to the octahedral face. Diamonds have a conchoidal fracture. The diamond can be cleaved in any plane as cleavage occurs readily parallel to the octahedral faces, giving four directions of possible cleavage. Diamonds occur in various colors like colorless (white) and pale yellow (off color or capes). However, colors of the diamond in blue, brown, red, orange, green, pink and deep-yellow are also found. Pink diamonds are due to to traces of manganese. Generally, the color of diamonds is widely thought to be due to lattice defects rather than trace elements.

A crystal named blue lace agate ia pale blue with white or darker lines. The crystal amber is Opaque or transparent resin with insects or vegetation trapped inside at times. The amber occurs in golden brown or yellow color and green amber occurs due to artificially coloring. An instance of transparent, pointed crystals is amethyst which occurs in purple to lavender color. The red-green colored bloodstone crystal appears as green quartz flecked with red or yellow jasper. The hematite crystal occurs in two colors namely silver, red and has vital properties like grounding and protecting. It appears as red or gray when unpolished, and shiny when polished.

Jade crystals that are translucent are termed jadeites and those that are creamy are termed nephrites. The colors in which jade crystals are available are green, orange, brown, blue, blue-green, cream, lavender, red and white. One instance of opaque and patterned crystal is jasper which is available in red, brown, yellow, green, blue and purple colors. The labradorite crystal which is available in colors grayish to black with blue and yellow is usually polished, dark until it catches the light and then turns iridescent blue or has gold flashes. Tiger’s Eye quartz crystal contains brown iron which makes it get the golden-yellow color. Crystals with higher degrees of symmetry tend to generate more form faces. Faces of particular forms commonly share unique physical or chemical attributes.

The absolute structure is the concept of relating some external macroscopic physical attribute of crystals. In fact, the powerful rays of color attribute of crystals speak about the frequency of the energy that they emit. Crystals have specific attributes attached to each of them as described above them. These special attributes of each crystal helps for a variety of specific usages of crystals and also for creating a stylish piece of jewelry using carefully chosen crystals.