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.