Jet

jet
Polished 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.

Jet Pictures

Beautiful jet brooch

Chemical Composition :

Carbon with impurities but not a mineral.

Classification / Type :

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

Crystal System / Forms :

None. Amorphous.

Cuts & Uses :

Carvings, beads, cabochons, etc.

Dispersion : None.
Hardness : 2.5 - 4
Lustre : Dull in rough; vitreous when polished.
Magnification :

None.

Optic Character :

Isotropic (S.R.)

Pleochroism : None.
Refractive Index / Birefringence :

1.66 (approx.) / Nil.

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)
Sources :

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

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

None.

Synthesis :

None.

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