Crystal & mineral guide
Coal
Organic sedimentary rock
Combustible organic rock — peat→lignite→bituminous→anthracite rank series.
Identify Coal with RockScanAbout Coal
Coal is an organic sedimentary rock formed from buried plant matter. Rank increases with heat/pressure from lignite to anthracite. Cleat fractures and low density aid ID. Jet (used in jewelry) is a related compact organic material. Industrial fuel and chemical feedstock historically.
Coal belongs in a crystal identifier workflow because photo cues — color zoning, crystal habit, and surface luster — combine with measurable traits like Mohs 1–2.5 (rank-dependent) and specific gravity 1.1–1.5. Use RockScan’s camera to get a first-pass ID, then confirm with the checklist below.
Coal properties
| Mohs hardness | 1–2.5 (rank-dependent) |
|---|---|
| Crystal system | Amorphous organic |
| Luster | Dull to vitreous (anthracite) |
| Color | Black to brown-black |
| Composition | Concentrated plant-derived carbonaceous matter |
| Formation | Burial and coalification of peat in swamps |
| Occurrence | Worldwide sedimentary basins; historic industrial regions |
| Specific gravity | 1.1–1.5 |
| Cleavage | None (may show cleat) |
How to identify Coal
- Lightweight black rock
- May soil fingers; combusts
- Anthracite is shinier and harder
Collector notes
- Carboniferous coal fueled the Industrial Revolution
- Jet is a compact form historically carved as gem
Value context: Commodity by rank and energy content; jet carvings are specialty jewelry.
Coal FAQ
How do you identify Coal?
Coal (Organic sedimentary rock) is typically recognized by black to brown-black color, dull to vitreous (anthracite) luster, Mohs hardness 1–2.5 (rank-dependent), and amorphous organic crystal system. RockScan can suggest Coal from a photo and surface these checks on the result card.
What is Coal made of?
Coal composition: Concentrated plant-derived carbonaceous matter. It forms via burial and coalification of peat in swamps and is found in Worldwide sedimentary basins; historic industrial regions.
Is Coal valuable?
Commodity by rank and energy content; jet carvings are specialty jewelry.
