amorphous Organic gems

Jet

Complex aromatic hydrocarbons (polycyclic aromatics + aliphatic components; compact lignite/bituminite); no fixed formula

Crystal Structure

CDL Notation

 #! Species: Jet (fossilised lignite)
#! System: Amorphous (organic mineraloid)
#! Habit: Massive compact carbonaceous material
amorphous[resinous]:{massive}

Crystal System amorphous

Point Group none

Crystal Forms (1)

{massive}

Quick Facts

Hardness

2.5

Specific Gravity

1.19

Refractive Index

1.64

Optical Character

Isotropic to near-isotropic (AGG)

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Physical Properties

Crystal Systemamorphous

Hardness (Mohs)2.5

Specific Gravity1.19

CleavageNone

FractureConchoidal (glossy fracture)

LustreGreasy to sub-vitreous

Optical Properties

Refractive Index1.64

Optical CharacterIsotropic to near-isotropic (AGG)

PleochroismNone

Colours

Intense black (only gem colour; occasionally very dark brown)

Localities

Whitby, North Yorkshire, England (primary source; Jurassic age ~175 Ma; Victorian mourning jewellery)Asturias, Spain (azabache; Santiago de Compostela pilgrimage jewellery)Phu Quoc Island, Vietnam (SG 1.24 and RI 1.66 confirmed)Turkey (Oltu, Erzurum; Oltu stone)Siberia, RussiaUSA (Utah, Colorado)

Common Inclusions

Wood-cell texture (compressed vascular tissue; visible at high magnification)Micro-cracks following wood grainRare plant cell fossils

Known Treatments

Carnauba wax/polish (surface)Lacquer coating (occasional)

Crystal Forms

massive

Diagnostic Features

Aromatic coal smell on hot-point test (primary diagnostic; distinguishes from French jet = no smell, vulcanite = sulfur smell); static electricity on rubbing (attracts tissue paper); SG 1.30-1.35 (very low); deformed wood-grain texture under microscope; RI ~1.66

Notes

Not an IMA mineral species; compact variety of lignite (sub-bituminous coal) derived from fossilised Araucaria-family driftwood. IMA-approved: N/A. SG 1.24 and RI 1.66 confirmed in Phu Quoc specimens by Le et al. 2022 (DOI 10.32508/stdj.v25i3.3968) [VERIFIED]. Wood-grain texture diagnostic: "deformed wood grain texture is visible under a microscope (400x and 100x)" — Le et al. 2022. Hot-point aromatic smell and static electricity tests from Read 7th ed. (DOI 10.4324/9780080507224) [PARTIALLY_SUPPORTED]. Key lookalikes: French jet (glass; no smell, high SG ~2.4-3.5), vulcanite (rubber; sulfur smell, SG ~1.15), bog oak (lighter, dark brown).