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.

Classification / Type: 

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

Colors / Varieties: 

Black, brownish.

Crystal System / Forms: 

None. Amorphous.

Hardness: 

2.5 - 4

Specific Gravity: 

1.20 - 1.30

Cleavage / Fracture: 

None / Conchoidal.

Optic Character: 

Isotropic (S.R.)

Lustre: 

Dull in rough; vitreous when polished.

Refractive Index / Birefringence: 

1.66 (approx.) / Nil.

Pleochroism: 

None.

Dispersion: 

None.

Magnification: 

None.

U.V. Fluorescence: 

Inert

Spectrum: 

None.

Treatment (Enhancement): 

None.

Specific Tests: 

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

Synthesis: 

None.

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)

Geological Occurrence: 

In sedimentary deposits, it is a fossilized wood.

Sources: 

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

Cuts & Uses: 

Carvings, beads, cabochons, etc.