Agatized algae forms when silica-rich fluids permeate ancient algal mats, preserving the delicate layered structures within chalcedony. Look for characteristic wavy, concentric banding or distinct 'biscuit' patterns that reveal the organic history of the specimen. It is highly sought after by lapidaries for its unique patterns when sliced and polished.
Is this agatized 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 agatized algae with a known reference. Agatized 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: Agatized (replaced by silica). 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: brown, red, tan, gray, white, yellow.
Often confused with
Agatized Algae vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside agatized algae
Minerals reported to co-occur with agatized 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
- Translucent
- Rarity
- Common
- Uses
- Lapidary, Collector
- Host rock
- sedimentary strata
- Organism
- Stromatolite: layered structures built by microbial mats, especially cyanobacteria
- Preservation
- Agatized (replaced by silica)
Where rockhounds find agatized algae
1 mapped spotsClassic worldwide localities
- Wyoming, USA
- Montana, USA
- Utah, USA
- Australia
- Mexico
Field-hunting tip
Where it forms: sedimentary strata. If you start seeing quartz, calcite, chalcedony in float, you are in the right ground. In the U.S., the densest reported localities are in Oklahoma. Start trip planning there.
More agatized algae photos
Common questions
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Find agatized algae on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
