Limestone is a sedimentary rock composed primarily of calcium carbonate, often derived from the skeletal fragments of marine organisms. It commonly exhibits a massive, fine-grained texture and will effervesce strongly when tested with dilute hydrochloric acid. Collectors should look for fossils within the rock, as limestone is one of the most common fossiliferous rocks found in nature.
Is this limestone?
4-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 limestone with a known reference. Limestone sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Pick out the mineralsComposition: Mostly calcite and aragonite (calcium carbonate); often contains fossils. Identify the two or three most abundant grains.
- 3Read the lusterHold the specimen under a strong light. Luster: dull to earthy.
- 4Match the color rangeCompare against the expected color range: white, gray, tan, yellow, black.
Often confused with
Limestone vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull to earthy on Limestone and vitreous to pearly on Dolomite.
How to tell apart: Luster reads dull to earthy on Limestone and subvitreous on Marble.
How to tell apart: Limestone is noticeably harder (Mohs 3 vs. 1).
Often found alongside limestone
Minerals reported to co-occur with limestone. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3
- Density
- 2.3-2.7 g/cm³
- Luster
- Dull to earthy
- Transparency
- Opaque
- Fluorescence
- Often fluorescent white or yellow under UV
- Rarity
- Common
- Uses
- Construction, Industrial, Decorative, Ornamental
- Host rock
- marine sedimentary basins
- Composition
- Mostly calcite and aragonite (calcium carbonate); often contains fossils
Where rockhounds find limestone
4 mapped spotsClassic worldwide localities
- France
- United States
- United Kingdom
- Germany
- China
Field-hunting tip
Where it forms: marine sedimentary basins. If you start seeing calcite, dolomite, quartz in float, you are in the right ground. In the U.S., the densest reported localities are in Florida, Michigan, Tennessee. Start trip planning there.
More limestone photos
Common questions
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Find limestone on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
