Jade gemstone

by Manisha G

jade-gemstoneJade is known as a mineral found out by the Chinese around 1000 BC and prized it above all other gemstones.

As a whole jade does not signify one mineral but has two different mineral as variety which does not have any relation in the chemical nature of the gemstones except in appearance.

1. Nephrite, belonging to the Amphibole group

2. Jadeite a member of the Pyroxene group

The amphiboles and the pyroxene are the important rock forming minerals.

Nephrite

It belongs to tremolite – actinolite series of amphibole family (light colours nearer to tremolite and darker to actinolite).

Chemical composition: Hydrated silicate of magnesium and calcium with magnesium and iron.

Crystal system: Monoclinic, Crystal structure: Fibrous, Habit: prismatic (aggregate)

Colours: Depends upon the amount of iron present. Whitish green to blackish brown, deep green. Usually they are coloured uniformly but occasionally spotted or veined.

Physical properties:

Hardness: 6.5

S.G.: 2.90 to 3.02 (mean – 3.00)

Transparency: Translucent to opaque

Lustre: greasy to waxy, cold to touch

Cleavage: Imperfect, under microscope in thin section fibres show cleavage cracks.

R.I.: 1.60-1.63 to 1.62-1.65 (1.62 mean) because of aggregate nature only vague reading at 1.62 can be seen.

Toughness: very tough, compact fibrouss mass.

Jadeite

Chemical composition: Sodium aluminium silicate

Crystal system: Mnoclinic (cryptocrystalline material)

Crystal structure: Granular

Colours: White, green yellow, orange to reddish brown or lavender, Chloromelanite – dark greenish black jadeite. The fine emrald green translucent varieties owing their colour to traces of chromium is highly priced.

Lustre: Greasy to waxy

Cleavage : Imperfect, Toughness – very tough compact granular mass, under Chelsea filter jadeite shows green but a dyed jadeite shows red colour.

Physical properties

Hardness: 7, S.G. – 3.30 to 3.36 (mean – 3.33) R.I. – 1.654 – 1.6677 (1.66 mean) because of aggregate nature only vague reading at 1.66 can be seen.

Transparency: Translucent to opaque.

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