Petrified algae, often found as stromatolites, are fossilized microbial mats that have been replaced by silica.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.
- 2Check the streakDrag the specimen across an unglazed porcelain plate. Petrified Algae leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Petrified Algae typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: tan, brown, gray, red, cream.
- 5Look at form & habitTypical habit: botryoidal, layered, massive, columnar.
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
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.7 g/cm³
- Streak
- White
- Luster
- Waxy
- Transparency
- Opaque
- Crystal habit
- Botryoidal, Layered, Massive, Columnar
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Sedimentary
- Typical price
- $10-100 per specimen
Where rockhounds find petrified algae
1 mapped spotsClassic worldwide localities
- Wyoming, USA
- Bolivia
- Australia
- Morocco
- Canada
Field-hunting tip
Look in sedimentary country — that is the host setting where petrified algae typically forms. If you start seeing quartz, chalcedony, calcite in float, you are in the right ground. Field specimens usually show a botryoidal, layered, massive, columnar habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Nevada — start trip planning there.
Common questions
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Find petrified algae on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
