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?
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 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 streakDrag the specimen across an unglazed porcelain plate. Agatized Fossil Shell leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agatized Fossil Shell typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: white, brown, red, gray, yellow, tan.
- 5Look at form & habitTypical habit: massive.
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
- Chemical formula
- SiO₂
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.7 g/cm³
- Streak
- White
- Luster
- Waxy
- Transparency
- Translucent
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Lapidary, Decorative
- Host rock
- Sedimentary Strata
Where rockhounds find agatized fossil shell
2 mapped spotsClassic worldwide localities
- Florida, USA
- Texas, USA
- Madagascar
- Morocco
- Australia
Field-hunting tip
Look in sedimentary strata country, the host setting where agatized fossil shell typically forms. If you start seeing quartz, calcite, pyrite in float, you are in the right ground. Field specimens usually show a massive habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Washington. Start trip planning there.
Common questions
How do you identify agatized fossil shell?+
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Find agatized fossil shell on the map
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