A stromatoporoid is a member of an extinct group of colonial marine organisms that were major reef-builders from the Ordovician through the Devonian. It typically appears as a layered or mamelon-textured calcareous mass, identified by its distinct grid-like internal structure under magnification.
Is this stromatoporoid?
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 stromatoporoid with a known reference. Stromatoporoid sits at Mohs 3-5, softer than the next harder reference, harder than the previous one.
- 2Name the organismDecide what left the fossil before worrying about the rock. Organism: Extinct sponges (clade Stromatoporoidea). Age: Middle Ordovician to Late Devonian.
- 3Check the preservationPreservation: Densely layered calcite 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.
- 5Match the color rangeCompare against the expected color range: tan, brown, gray, white.
Often confused with
Stromatoporoid vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside stromatoporoid
Minerals reported to co-occur with stromatoporoid. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 3-5
- Density
- 2.6-2.8 g/cm³
- Luster
- Dull
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Collector, Educational, Decorative
- Host rock
- sedimentary limestone or dolostone
- Organism
- Extinct sponges (clade Stromatoporoidea)
- Age
- Middle Ordovician to Late Devonian
- Preservation
- Densely layered calcite skeleton
Where rockhounds find stromatoporoid
5 mapped spotsClassic worldwide localities
- Canada
- United Kingdom
- Estonia
- United States
- Czech Republic
Field-hunting tip
Where it forms: sedimentary limestone or dolostone. 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 Michigan. Start trip planning there.
More stromatoporoid photos
Common questions
How do you identify stromatoporoid?+
Where is stromatoporoid found?+
Can I find stromatoporoid in the United States?+
What rocks look like stromatoporoid?+
What minerals are found with stromatoporoid?+
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Find stromatoporoid on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
