Agatized fossils are biological remains, such as coral, bone, or shells, that have been preserved through the replacement of original structures by microcrystalline silica. Collectors look for high levels of translucency and well-preserved morphological detail, often found in sedimentary deposits where groundwater rich in dissolved silica has permeated the specimen over millions of years.
Is this agatized fossils?
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 fossils with a known reference. Agatized Fossils 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 Fossils leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Agatized Fossils typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: brown, red, yellow, white, gray, multicolored.
- 5Look at form & habitTypical habit: massive.
Often confused with
Agatized Fossils vs. its common look-alikes — and how to tell them apart in the field.
Often found alongside agatized fossils
Minerals reported to co-occur with agatized fossils. 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
- Vitreous
- Transparency
- Translucent
- Crystal habit
- Massive
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Sedimentary Strata
- Typical price
- $5-50 for small specimens, $100-500+ for display pieces
Where rockhounds find agatized fossils
3 mapped spotsClassic worldwide localities
- Arizona, USA
- Madagascar
- Brazil
- Indonesia
- Patagonia, Argentina
Field-hunting tip
Look in sedimentary strata country — that is the host setting where agatized fossils 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 Tennessee, Georgia — start trip planning there.
Common questions
How do you identify agatized fossils?+
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Find agatized fossils on the map
RockHoundR shows mapped rockhounding spots, access rules, and lets you log every find.
