Jet

Jet is a black organic substance which is a fossilized variety of brown coal, formed as a result of the compaction of driftwood over millions of years.

Jet has a dull lustre in rough form while vitreous lustre after polished. It is a stone with low S.G. (1.20 – 1.30) but high R.I. (1.66). It is the key identifying feature of jet for separating it from its simulants.

Chemical Composition : Carbon with impurities but not a mineral.

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Classification / Type : 

A compact form of coal (further heat and pressure makes it more tough)

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Crystal System / Forms : 

None. Amorphous.

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Cuts & Uses : 

Carvings, beads, cabochons, etc.

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Dispersion : None.

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Hardness : 2.5 - 4

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Lustre : Dull in rough; vitreous when polished.

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Magnification : 

None.

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Optic Character : 

Isotropic (S.R.)

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Pleochroism : None.

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Refractive Index / Birefringence : 

1.66 (approx.) / Nil.

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Simulants (with separation tests) :

• Anthracite (black streak)
• Glass (R.I., S.G., inclusions)
• Plastic (R.I., hot point, structure)
• Black stained chalcedony (R.I., S.G., banding)
• Obsidian (R.I., S.G., inclusions)
• Vulcanite – hard rubber (rotten egg smell to a hot point)

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Sources : 

England, Spain, France, U.S.A., Germany, Russia.

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Specific Tests :

• Gives a strong coal or oily odor to a hot point.
• Brown streak color on a porcelain plate.

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Spectrum : 

None.

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Synthesis : 

None.