An agatized fossil shell forms when the original organic material is gradually replaced by microcrystalline silica, preserving intricate internal and external structure. It is sought after for its durability, fine detail, and often colorful, translucent patterning, and occurs in sedimentary environments where mineral-rich groundwater has permeated ancient shell beds.
Is this agatized fossil shell?
4-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 fossil shell with a known reference. Agatized Fossil Shell sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
- 2Check the preservationPreservation: Agatized: silica-rich fluids replace the shell. That controls the weight, the hardness and how the piece takes a polish.
- 3Read the lusterHold the specimen under a strong light. Luster: waxy.
- 4Match the color rangeCompare against the expected color range: white, brown, red, gray, yellow, tan.
Often confused with
Agatized Fossil Shell vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside agatized fossil shell
Minerals reported to co-occur with agatized fossil shell. 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
- Collector, Lapidary, Decorative
- Host rock
- sedimentary strata
- Preservation
- Agatized: silica-rich fluids replace the shell
Where rockhounds find agatized fossil shell
2 mapped spotsClassic worldwide localities
- Florida, USA
- Texas, USA
- Madagascar
- Morocco
- Australia
Field-hunting tip
Where it forms: sedimentary strata. If you start seeing quartz, calcite, pyrite in float, you are in the right ground. In the U.S., the densest reported localities are in Washington. Start trip planning there.
Common questions
How do you identify agatized fossil shell?+
Where is agatized fossil shell found?+
Can I find agatized fossil shell in the United States?+
What rocks look like agatized fossil shell?+
What minerals are found with agatized fossil shell?+
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Find agatized fossil shell on the map
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