RocksdayCoal vs Jet
How to tell them apart
A rock formed from buried, compressed plant material — ancient swamp forests turned to stone.
Photo: Amcyrus2012, CC BY 4.0
A hard, compact black lignite — fossil wood — that takes a mirror polish.
Photo: Geni, CC BY-SA 4.0
Quick tests
- Texture: Coal is a rock — a mix of grains or minerals; Jet is a single mineraloid.
Key differences
- Coal is dull and crumbly.
Side by side
| Property | Coal | Jet |
|---|---|---|
| Type | Sedimentary rock | Mineraloid |
| Mohs hardness | 2–3 | 2.5–4 |
| Luster | Dull to submetallic | Velvety to vitreous (polished) |
| Streak | — | Brown |
| Colors | Black, Brown | Black |
| Crystal system / structure | Organic, layered | Amorphous (organic) |
| Specific gravity | 1.1–1.8 | 1.3–1.4 |
| Found in | Powder River Basin, Wyoming; Appalachia | Whitby, England; Asturias, Spain |
Properties that are the same for both are grayed out.
How to identify coal
- Black and very light for a rock.
- Leaves black dust on hands.
- Layered, with blocky or curved breaks.
- Burns.
Structure: Organic, layered
Full Coal guide →How to identify jet
- Jet black, light and warm to the touch.
- Brown streak.
- Smells like coal when a hot needle touches it.
Structure: Amorphous (organic)
Full Jet guide →More comparisons
Could you tell them apart from a blurry close-up?
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