Crinoidal limestone is a sedimentary rock composed primarily of fossilized stem segments and plates from crinoids, ancient echinoderms known as sea lilies. Look for characteristic circular or star-shaped fossil fragments embedded within a calcium carbonate matrix, which are often visible on weathered surfaces or polished slabs. This rock formed in shallow marine environments and is commonly found in geologic strata from the Paleozoic era.
Is this crinoidal 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 crinoidal limestone with a known reference. Crinoidal Limestone sits at Mohs 3, softer than the next harder reference, harder than the previous one.
- 2Pick out the mineralsComposition: Fossiliferous limestone rich in crinoid remains, whose stems are columns of porous calcareous ossicles. Identify the two or three most abundant grains.
- 3Read the lusterHold the specimen under a strong light. Luster: dull.
- 4Match the color rangeCompare against the expected color range: gray, tan, white, brown.
Often confused with
Crinoidal Limestone vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside crinoidal limestone
Minerals reported to co-occur with crinoidal limestone. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3
- Density
- 2.5-2.7 g/cm³
- Luster
- Dull
- Transparency
- Opaque
- Fluorescence
- Often fluorescent yellow or white
- Rarity
- Common
- Uses
- Decorative, Construction, Collector
- Host rock
- marine sedimentary deposits
- Composition
- Fossiliferous limestone rich in crinoid remains, whose stems are columns of porous calcareous ossicles
Where rockhounds find crinoidal limestone
Classic worldwide localities
- USA
- United Kingdom
- Germany
- Belgium
- France
Field-hunting tip
Where it forms: marine sedimentary deposits. If you start seeing calcite, dolomite, quartz in float, you are in the right ground.
Common questions
How do you identify crinoidal limestone?+
Where is crinoidal limestone found?+
What rocks look like crinoidal limestone?+
What minerals are found with crinoidal limestone?+
What kind of rock does crinoidal limestone form in?+
What is crinoidal limestone used for?+
Find crinoidal limestone on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
