Petrified algae, often found as stromatolites, are fossilized microbial mats that have been replaced by silica. They are prized by collectors for their distinctive layered or cauliflower-like internal banding and earthy, multi-toned color patterns.
Is this petrified algae?
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 petrified algae with a known reference. Petrified Algae sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
- 2Name the organismDecide what left the fossil before worrying about the rock. Organism: Stromatolite: layered structures built by microbial mats, especially cyanobacteria.
- 3Check the preservationPreservation: Petrified by silica replacement. That controls the weight, the hardness and how the piece takes a polish.
- 4Read the lusterHold the specimen under a strong light. Luster: waxy.
- 5Match the color rangeCompare against the expected color range: tan, brown, gray, red, cream.
Often confused with
Petrified Algae vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside petrified algae
Minerals reported to co-occur with petrified algae. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.7 g/cm³
- Luster
- Waxy
- Transparency
- Opaque
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- sedimentary
- Organism
- Stromatolite: layered structures built by microbial mats, especially cyanobacteria
- Preservation
- Petrified by silica replacement
Where rockhounds find petrified algae
1 mapped spotsClassic worldwide localities
- Wyoming, USA
- Bolivia
- Australia
- Morocco
- Canada
Field-hunting tip
Where it forms: sedimentary. If you start seeing quartz, chalcedony, calcite in float, you are in the right ground. In the U.S., the densest reported localities are in Nevada. Start trip planning there.
Common questions
How do you identify petrified algae?+
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Can I find petrified algae in the United States?+
What rocks look like petrified algae?+
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Find petrified algae on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
