A silicified fossil is an organic remain replaced molecule by molecule by silica during fossilization. Look for preserved cellular structure, growth rings in wood, or fine surface texture on shell and bone. It occurs in sedimentary layers where silica-rich groundwater has permeated organic matter.
Is this silicified fossil?
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 silicified fossil with a known reference. Silicified Fossil 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. Silicified Fossil leaves a white streak.
- 3Read the lusterHold the specimen under a strong light. Silicified Fossil typically shows a vitreous luster.
- 4Match the color rangeCompare against the expected color range: brown, red, yellow, white, gray, black.
- 5Look at form & habitCrystal system: trigonal. Typical habit: pseudomorph.
Often confused with
Silicified Fossil vs. its common look-alikes, and how to tell them apart in the field.
How to tell apart: Luster reads vitreous on Silicified Fossil and waxy on Chalcedony.
How to tell apart: Luster reads vitreous on Silicified Fossil and waxy on Agate.
How to tell apart: Luster reads vitreous on Silicified Fossil and waxy on Jasper.
Often found alongside silicified fossil
Minerals reported to co-occur with silicified fossil. 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
- 2.5-2.7 g/cm³
- Streak
- White
- Luster
- Vitreous
- Transparency
- Translucent
- Crystal system
- Trigonal
- Crystal habit
- Pseudomorph
- Cleavage
- None
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- Sedimentary Deposits
Where rockhounds find silicified fossil
1 mapped spotsClassic worldwide localities
- Petrified Forest National Park, USA
- Madagascar
- Indonesia
- Argentina
- Egypt
Field-hunting tip
Look in sedimentary deposits country, the host setting where silicified fossil typically forms. If you start seeing quartz, chalcedony, goethite in float, you are in the right ground. Field specimens usually show a pseudomorph habit, so train your eye for that shape before scanning the outcrop. In the U.S., the densest reported localities are in Kentucky. Start trip planning there.
Common questions
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Find silicified fossil on the map
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