Stromatoporoids are an extinct group of colonial marine organisms that were major reef-builders from the Ordovician to the Devonian periods. They typically appear as layered or mamelon-textured calcareous masses that are easily identified by their distinct grid-like internal structure when viewed under magnification.
Is this stromatoporioids?
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 stromatoporioids with a known reference. Stromatoporioids sits at Mohs 3-5, softer than the next harder reference, harder than the previous one.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Stromatoporioids leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Stromatoporioids typically shows a dull luster.
- 4Match the color rangeCompare against the expected color range: tan, brown, gray, white.
- 5Look at form & habitTypical habit: massive, laminar, columnar, hemispherical.
Often confused with
Stromatoporioids vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside stromatoporioids
Minerals reported to co-occur with stromatoporioids. 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
- Streak
- White
- Luster
- Dull
- Transparency
- Opaque
- Crystal habit
- Massive, Laminar, Columnar, Hemispherical
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Educational, Decorative
- Host rock
- Sedimentary Limestone or Dolostone
- Typical price
- $5-100 depending on size and preservation
Where rockhounds find stromatoporioids
1 mapped spotsClassic worldwide localities
- Canada
- United Kingdom
- Estonia
- United States
- Czech Republic
Field-hunting tip
Look in sedimentary limestone or dolostone country, the host setting where stromatoporioids typically forms. If you start seeing calcite, dolomite, quartz in float, you are in the right ground. Field specimens usually show a massive, laminar, columnar, hemispherical habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Iowa. Start trip planning there.
More stromatoporioids photos
Common questions
How do you identify stromatoporioids?+
Where is stromatoporioids found?+
Can I find stromatoporioids in the United States?+
How much is stromatoporioids worth?+
What rocks look like stromatoporioids?+
What minerals are found with stromatoporioids?+
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Find stromatoporioids on the map
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