Some Important Properties of Gemstones
Some important properties of gemstones are the things which set apart them from other ordinary glass like, glittering stones of earth. They are as follows,
Crystal habit, Crystal system, Colour, Hardness, Refractive index, Lustre, Cleavage, Density, Specific gravity and Dispersion.
It can be defined as the unique growth of the particular mineral crystal which may vary with various growth conditions like temperature and pressure. When one mineral is replaced by another by preserving the original growth, it is called as Pseudomorphous replacement. Most of gemstones are not found as perfectly formed single crystals but are found aggregate of several crystals grown together in one mass,
The crystal habit is influenced by the following factors as follows,
1. Crystal twinning,
2. Crystal growth conditions ( temperature and pressure)
3. Trace impurities.
For eg. Precious stones like diamonds have their growth in very deep part of earth at very high pressure and high temperature. Most of the diamonds are free from metallic impurities and they are having elemental carbon in crystalline form. But some times they appear in different colours by the nitrogen impurities found in them.
A crystal system is a category of space groups which characterize the symmetry of structure in 3 dimensions. (i. e.) x axis, y axis and z axis. This is applied to categorize crystals. For example, diamond which is also called as cubic zirconia is in cubic system. The unit cell is in cubic shape.
If all the gemstones were available in colorless form they would not have reached this much of popularity as they are having in their colorful form. The different colors are giving special attraction to all variety of gemstones. For eg. chromium found in Aluminium oxides of corundum, ruby is giving dark pink color to them. Emerald is getting it's beautiful color with the addition of Barium.
This measures the scratch resistance of various minerals through the ability of harder material to scratch softer material. It was created in 1812 by German mineralogist Friedrich Mohs. However it is one of the several definitions of hardness in material science. As we all know that Diamond is the hardest of all the gemstones with a Mohs scale of 10.
It is a measure of how much the speed of the light is reduced inside the medium. For eg. refractive index for a glass is 1.5. It can be obtained by the formula n = c / vp
n = refractive index
c = speed of the lght in air or vaccum
vp = velocity of the light in medium.
The refractive index of glass shows the speed of light in it is 0.67 times the
speed of the same in vaccum or air.
It describe the way of light interacts with the surface of a crystal. For eg. diamond is said to have adamantine lustre and pyrite is having metallic lustre.
This is the tendency of crystalline materials to split along definite planes creating smooth surfaces. For eg.
Basal cleavage - parallel to the base of the crystal.
Cubic cleavage - parallel to the faces of cube.
Diagonal cleavage - parallel to a diagonal plane.
Density is the mass per unit volume. The ratio of the mass of the material to it's volume. For eg. an iron ball is heavier than a rubber ball. As the most of the gemstones are metallic oxides and silicates they are found to be heavier than ordinary stones of earth.
It is the ratio of the density of the material to the density of water.
It means the phase velocity of light on it's frequency.
v = c / n
c = velocity of light in air or vacuum.
n = refractive index.
v = phase velocity of the light.
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