Comparison · Sedimentary Rocks vs Organic Gem Materials
Coal vs Jet
Coal and Jet are easy to confuse. Jet is harder (Mohs 3) than Coal (Mohs 1–2.5), so Jet will scratch Coal and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Below is a side-by-side comparison of their properties and the quick tests that separate them.
Key differences between Coal and Jet
- Jet is harder (Mohs 3) than Coal (Mohs 1–2.5), so Jet will scratch Coal and not the other way round. A fingernail (Mohs 2.5) scratches it easily.
- Streak color differs: Coal leaves a black to brownish black streak on unglazed porcelain, Jet leaves brown.
- Luster is different: Coal is dull (lignite) to vitreous (anthracite) while Jet is waxy.
- Hold a thin edge to the light: Coal is Opaque, Jet is opaque.
- Well-formed crystals give it away: Coal is Amorphous, Jet is amorphous.
Coal vs Jet properties
| Property | Coal | Jet |
|---|---|---|
| Type | Sedimentary Rocks | Organic Gem Materials |
| Mohs hardness | 1–2.5 | 3 |
| Luster | Dull (lignite) to vitreous (anthracite) | waxy |
| Streak | Black to brownish black | Brown |
| Transparency | Opaque | opaque |
| Specific gravity | 1.1–1.8 | 1.3 |
| Crystal system | Amorphous | amorphous |
| Common colors | Black, Brownish black | Black, Dark brown |
| Rarity | common | uncommon |
| Typical specimen value | $1–$75+ | $5–$300+ |
Which is more valuable?
Jet is usually the more valuable of the two: a typical collector specimen runs about $40 against $10 for Coal, and premium Jet can reach $300 or more.
About Coal
Coal is a combustible sedimentary rock composed mostly of carbon along with hydrogen, oxygen, and trace minerals, formed from the compaction and chemical alteration of ancient plant material. Unlike true minerals, it lacks a fixed crystal structure or chemical formula, and its properties vary with rank, the degree of transformation from the original plant matter. It ranges from soft, brown lignite to hard, glossy anthracite.
About Jet
Jet is a compact, lightweight black organic gem material formed from fossilized wood. It takes a high polish, feels warm to the touch, and has been used for mourning jewelry and ornaments since antiquity.
Coal vs Jet FAQ
Is Coal the same as Jet?
No. Coal is a sedimentary rock while Jet is a organic gem material. Jet is harder (Mohs 3) than Coal (Mohs 1–2.5), so Jet will scratch Coal and not the other way round. A fingernail (Mohs 2.5) scratches it easily.
How can you tell Coal from Jet?
Jet is harder (Mohs 3) than Coal (Mohs 1–2.5), so Jet will scratch Coal and not the other way round. A fingernail (Mohs 2.5) scratches it easily. Streak color differs: Coal leaves a black to brownish black streak on unglazed porcelain, Jet leaves brown. Luster is different: Coal is dull (lignite) to vitreous (anthracite) while Jet is waxy.
Which is harder, Coal or Jet?
Jet is harder: Mohs 3 against Mohs 1–2.5 for Coal.
Which is more valuable, Coal or Jet?
Jet is usually the more valuable of the two: a typical collector specimen runs about $40 against $10 for Coal, and premium Jet can reach $300 or more.
