Coral consists of the skeletal remains of colonial marine organisms primarily composed of calcium carbonate. Collectors often seek out branching or botryoidal structures, which can be polished to a high luster for jewelry. Note that modern coral harvesting is often restricted to protect reef ecosystems, making vintage specimens highly valued.
Is this coral?
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 coral with a known reference. Coral sits at Mohs 3-4, softer than the next harder reference, harder than the previous one.
- 2Name the organismDecide what left the fossil before worrying about the rock. Organism: Corals (class Anthozoa, phylum Cnidaria).
- 3Check the preservationPreservation: Calcium carbonate skeleton. That controls the weight, the hardness and how the piece takes a polish.
- 4Read the lusterHold the specimen under a strong light. Luster: dull to waxy.
- 5Match the color rangeCompare against the expected color range: white, pink, red, orange, brown.
Often confused with
Coral vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads dull to waxy on Coral and vitreous, pearly in aggregates on Rhodochrosite.
How to tell apart: Rhodonite is the harder of the two (Mohs 5.5-6.5 vs. 3-4); luster reads dull to waxy on Coral and vitreous, somewhat pearly on cleavages on Rhodonite.
Often found alongside coral
Minerals reported to co-occur with coral. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3-4
- Density
- 2.6-2.7 g/cm³
- Luster
- Dull to waxy
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Jewelry, Lapidary, Decorative
- Host rock
- marine sedimentary deposits
- Organism
- Corals (class Anthozoa, phylum Cnidaria)
- Preservation
- Calcium carbonate skeleton
Where rockhounds find coral
8 mapped spotsClassic worldwide localities
- Mediterranean Sea
- Japan
- Taiwan
- Red Sea
- Australia
Field-hunting tip
Where it forms: marine sedimentary deposits. If you start seeing calcite, aragonite in float, you are in the right ground. In the U.S., the densest reported localities are in Wisconsin, Florida, Illinois. Start trip planning there.
More coral photos
Common questions
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Find coral on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
