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

Jet Properties

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.