VARIETY OF GEM STONES AND GEMS

Gem stones, also called as precious stones, are naturally available rare ston-

-es of earth. They get different names according to the chemicals present

in them. Some important varieties of gem stones are diamond, corundum,

beryl, coral and pearl.

Diamond is a precious stone made of pure carbon. It is allotrope form of

carbon and noted for it's hardness. The diamonds are white or pale yellow

in colour. Less often they are also available in blue, green, yellow and black.

Under the deep part of our earth, extreme pressure and temperature change

carbon to glittering diamonds. Diamond's crystal system is cubic, hardness

in Mohs scale is 10, refractive index is 2.4175, density is 3.5 gm/cc and

melting point is 3,547 degree centigrade. About 26 tonnes of natural diamond

is mined per year from all over the world. It is widely used in jewelry and optical

industries.

These are naturally found stones made of Aluminium trioxide. Ruby and

Sapphire are two important varieties of corundum.

It is dark pink or red in colour, some-

-times available in brownish or pur-

-plish. It is a Cr containing Alumini-

-um trioxide. It 's crystal system is

trigonal. It's hardness is, next to

diamond, 9 in Mohs scale. The ref-

-ractive index is 1.762 and it's melt-

-ing point is 2050 degree centigrade.

It can not be considered as a precious

stone alike diamond.

It is also a semi precious stone made

of Aluminium trioxide and available in

many colours except red. It's crystal

system is trigonal and hardness in

Moh scale is 9 and refractive index

is 1.762. It's melting point is around

2,000 degree centigrade.

These are beryllium containing Aluminium silicate compounds. These are

classified to semi precious stones. Available in green, red, yellow and pink.

Emerald, Aquamarine, Bixbite and Morganite are some of Beryl stones.

Emerald

This is a variety of mineral beryl. This is green in colour and have hardness

of 7.5 - 8. There are some traces of chromium in this compund. It's crystal

system is hexagonal and refractive index is 1.576 - 1.582

Acquamarine

This is also one of the Beryllium

containing Aluminium silicates and

having delicate blue color. It's cry-

-stal system is hexagonal and has

hardness of 7.5 - 8. It's refractive

index ranges from 1.57 - 1.58. It has wide range uses in jewelry industries.

Bixbite

This is a red variety of Beryl. Avai-

-lable in orange red to purple red.

Crystal system is hexagonal and

hardness in Mohs scale is 7.5 - 8.

It's refractive index is1.567 - 1.580

and has melting point around 2000

degree centigrade. Manganese pre-

-sents in it gives red color to it.

Morganite

This is a light pink colored Bery-

-llium containing Aluminium sili-

-cate compound. It's crystal system

is hexagonal and hardness varies

as 7.5 - 8. It's refractive index is

1.57 - 1.58. Right side shown is

one of the larger morganite retri-

-eved from Elizabeth mine in Pala, California in the year 2005

These are skeletal remains of

marine organisms(Anthozoa)

and have blood like red color.

Main chemical content is CaCo3

and it is considered as a semi

precious gem. These are widely

used in jewelry. Largely found in Great Barrier Reef off coast of Queen island

and Australia.

It is a pale white colored hard object produced with in soft tissues of a living

shell mollusk. CaCo3 is the main chemical content. The good quality of pearl

is valued as gem stone. It is naturally available in the seas. However cultured

pearls are more valuable than natural ones. pearls are widely used in jewelry

and medicines.