Coal is a combustible sedimentary rock formed from ancient plant matter that has been buried and subjected to heat and pressure over millions of years. It varies significantly in quality and carbon content, ranging from soft brown lignite to hard, shiny anthracite. Collectors typically look for specimens showing clear plant impressions or distinct layering.
Is this coal?
5-step field checkRun through these checks against the specimen in your hand. The more boxes tick, the more confident the ID.
- 1Test the hardnessTry to scratch coal with a known reference. Coal sits at Mohs 0.5-2.5, softer than the next harder reference, harder than the previous one.
- 2Read the textureLook at a fresh break with a hand lens. Texture: Forms layers (seams); bituminous coal often banded bright and dull.
- 3Pick out the mineralsComposition: Carbon-rich rock from plant material; bituminous coal is about 84 percent carbon. Identify the two or three most abundant grains.
- 4Read the lusterHold the specimen under a strong light. Luster: dull to submetallic.
- 5Match the color rangeCompare against the expected color range: black, brown.
Often confused with
Coal vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside coal
Minerals reported to co-occur with coal. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 0.5-2.5
- Density
- 1.1-1.5 g/cm³
- Luster
- Dull to submetallic
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Industrial, Fuel, Collector
- Host rock
- sedimentary coal seams
- Texture
- Forms layers (seams); bituminous coal often banded bright and dull
- Composition
- Carbon-rich rock from plant material; bituminous coal is about 84 percent carbon
Where rockhounds find coal
1 mapped spotsClassic worldwide localities
- USA
- China
- Australia
- India
- Germany
Field-hunting tip
Where it forms: sedimentary coal seams. If you start seeing pyrite, siderite, kaolinite in float, you are in the right ground. In the U.S., the densest reported localities are in Montana. Start trip planning there.
Common questions
How do you identify coal?+
Where is coal found?+
Can I find coal in the United States?+
What rocks look like coal?+
What minerals are found with coal?+
What kind of rock does coal form in?+
What is coal used for?+
Find coal on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
