Agatized clams are fossilized bivalve shells that have been replaced by microcrystalline silica, preserving the original structure while turning the fossil into gemstone material. They are prized by collectors for their intricate internal banding and varied coloration, often found in sedimentary deposits where groundwater rich in silica has percolated through the shells.
Is this agatized clams?
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 clams with a known reference. Agatized Clams 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 Clams leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agatized Clams typically shows a waxy luster.
- 4Match the color rangeCompare against the expected color range: white, gray, brown, tan, red, yellow.
- 5Look at form & habitCrystal system: trigonal. Typical habit: massive.
Often confused with
Agatized Clams vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside agatized clams
Minerals reported to co-occur with agatized clams. 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 system
- Trigonal
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Collector, Lapidary, Decorative
- Host rock
- Sedimentary Layers
- Typical price
- $5-100 per specimen
Where rockhounds find agatized clams
3 mapped spotsClassic worldwide localities
- Florida, USA
- California, USA
- Madagascar
- Oregon, USA
Field-hunting tip
Look in sedimentary layers country — that is the host setting where agatized clams typically forms. If you start seeing quartz, calcite, chalcedony 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 Utah — start trip planning there.
Common questions
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Find agatized clams on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
