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Crystal Lattice Structures @ Jewel Info 4 U
By:Ritika
Summary: The various
gemstones take their shape and
structure based on their unique
crystalline structure that each
gemstone possesses. These
crystalline structures of each
gemstone is based and made from a
mixture of different elemental
compounds. Thus the atomic structure
associated with elemental building
blocks contributes towards the shape
of a crystal or gemstone.
Crystal Structure and Technical
Terms
 The various attributes associated
with a gemstone like its symmetry,
geometric shape, optical properties
and cleavage planes are all
determines and based on the crystal
structure of a gemstone. The
technical term Crystal Habit is used
to depict the growth pattern of
crystal.
Crystal's Lattice:
The grouping of crystal structures
constitutes a crystal system. These
are divided and grouped based on the
axial system which describe the
crystal lattice. A lattice denotes
regular array of lattice points in
three dimensions. That is a crystal
lattice is nothing but atoms
arranged in a symmetrical pattern on
a three dimensional network fashion.
The structure formed by connecting
the eight lattice points is a
parallelepiped which is technically
termed as a crystallographic unit
cell.
The crystal is a repeating array and
its structure is determined by the
following two properties namely:
- pattern of repetition which is
termed as the lattice type
- what is repeated which is termed
as the unit cell
Types of Crystal Systems:
Each crystal system is arranged in a
set of three axes geometric system.
Each crystal system takes a unique
shape based on the unique
geometrical arrangement of each
crystal system on the three axes.
There are seven types of crystal
systems and they are as below:
- Isometric System
-
Hexagonal System
- Tetragonal System
- Rhombohedric (Trigonal) System
- Orthorhombic System
- Monoclinic System
- Triclinic System
The above seven crystal systems are
listed in order of their decreasing
symmetry. The geometric arrangement
of the individual lattice points
within each of the seven crystal
systems described above is termed as
Bravais lattices and there are
fourteen distinct Bravais lattices.
Crystal Lattice Structures:
The popular crystal lattice
structures are
- Simple Cubic
- Cubic Close Packed Crystals
- Body-Centered Cubic
- Hexagonal Close-Packed Crystals
- Carbon and Related Structures
- Manganese Structures
- The Laves Phase Structures
- Perovskite and Related Structures
- Quartz and Related Structures
- Sulfur and its compounds
- Structures of the Lanthanides,
Actinides and Their Compounds
- IIIb-VIIb Structures
- Binary Pnma Alloy Structures
- and Other Crystal Structures
Cubic unit cell and Simple Cubic Unit Cell:
The elements which constitute a
cubic unit cell are six square faces
and three equal non-coplanar edges.
That is if the sides are denotes by
x, y, z then a cubic unit cell has
the following characteristics namely
x=y=z
The volume of the cubic unit cell is
denoted as x3
Simple Cubic unit cell is also
denoted as SC in short. The simple
cubic unit cell has one lattice
point present in each of the eight
corners of a cube. If the lattice
points are present only at the eight
corners of the cube then it is
termed technically as primitive.
Cubic Close Packed Crystals:
Crystalline structures associated in
a closed packed cubic lattice are
termed as cubic close packed
crystals.
Body-Centered Cubic:
Body-Centered Cubic is also referred
as BCC in short consist of a single
host atom at each corner of the
cubic unit cell and a single atom in
the cell center. The arrangement in
BCC is such that each of these atoms
touches eight other host atoms along
the body diagonal of the cube.
Hexagonal Close-Packed Crystals:
Hexagonal Close-Packed Crystals is
also termed as HCP in short. In this
structure the arrangement of plane
is in such a fashion such that atoms
in successive planes associate in a
triangular groove with the preceding
plane.
Carbon and Related Structures:
Crystalline lattice refers to the
atoms in a crystal that are arranged
in a regular repeating pattern. The
property or attribute of a crystal
is highly determined by its lattice.
For instance both graphite and
diamond constitute carbon as its
major element or atom. But both
graphite and diamond differs in its
properties which is based on how the
atom namely carbon is arranged in
both. That is we can see that
graphite which is black in color has
the attribute of being soft and also
acts as a good lubricant. This
clearly depicts that atoms in
graphite could be separated easily.
In contrast the attribute of diamond
are that it is strong and extremely
hard and is also transparent at the
same time. This clearly shows that
the atoms in diamond could not be
separated easily as it is strongly
bounded.
Manganese Structures:
There are several structures in
which Manganese is available and the
most rarest forms are termed as aMn
and ßMn.
The Laves Phase Structures:
The elements arranged in Laves Phase
Structure are in the order as AB2.
In this the atom A is arranged in
the similar way as in crystal like
diamond and the atom B is arranged
in the shape of tetrahedra around
the atom A.
Perovskite and Related
Structures:
The crystal structure like
Perovskite structure have
ferroelectric attribute. The
structure of crystal along with this
attribute enables these to become
permanently polarized when these are
subjected to electric field of
sufficient magnitude.
Quartz and Related Structures:
The chemical symbolic representation
of Quartz is SiO2 and this exists in
different forms. The crystal
structure in which alpha Quartz is
present is termed as Trigonal. The
Trigonal crystal system has totally
four axes. Of these four axes three
axes are of equal length and they
lie at an angle of 120° from each
other. The fourth axes are either
longer or shorter in length but
exist at a right angle toward the
other corners.
Structures of the Lanthanides,
Actinides and their Compounds:
The Lanthanides, Actinides and their
Compounds exist in various
structures. Some of the rare forms
among these are namely Cf, aPu, ßPu
and so on.
Other Crystal Structures:
There are other crystal structures
as well like Trigonal omega phase
referred to as C6, Cuprites referred
to as C3 and so on which do not fit
in any of the above described.
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