Agatized fossil shells occur when original organic material is gradually replaced by microcrystalline silica, preserving intricate internal and external structures. These specimens are highly sought after for their durability, intricate detail, and often colorful, translucent patterns. They are frequently found in sedimentary environments where mineral-rich groundwater has permeated ancient shell beds.
Is this agatized fossil shells?
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 shells with a known reference. Agatized Fossil Shells 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 Shells leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agatized Fossil Shells 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 Shells vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside agatized fossil shells
Minerals reported to co-occur with agatized fossil shells. 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
- Typical price
- $10-100 per specimen
Where rockhounds find agatized fossil shells
2 mapped spotsClassic worldwide localities
- Florida, USA
- Texas, USA
- Madagascar
- Morocco
- Australia
Field-hunting tip
Look in sedimentary strata country — that is the host setting where agatized fossil shells 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
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Find agatized fossil shells on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
