Silicified oolite consists of spherical grains called ooids that have been replaced or cemented by microcrystalline silica. Collectors look for the distinct 'fish-egg' texture visible in cross-sections, which polishes beautifully for lapidary work.
Is this silicified oolite?
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 oolite with a known reference. Silicified Oolite sits at Mohs 6.5-7, softer than the next harder reference, harder than the previous one.
- 2Name the organismDecide what left the fossil before worrying about the rock. Organism: Ooids (spherical grains of concentric layers), not an organism.
- 3Check the preservationPreservation: Silica replaces the original carbonate by the same volume. That controls the weight, the hardness and how the piece takes a polish.
- 4Read the lusterHold the specimen under a strong light. Luster: waxy.
- 5Match the color rangeCompare against the expected color range: white, gray, brown, tan, red.
Often confused with
Silicified Oolite vs. its common look-alikes, and how to tell them apart in the field.
Often found alongside silicified oolite
Minerals reported to co-occur with silicified oolite. Spotting these in float or country rock is a strong cue you are in the right ground.
All properties
- Mohs hardness
- 6.5-7
- Density
- 2.6-2.65 g/cm³
- Luster
- Waxy
- Transparency
- Translucent
- Rarity
- Common
- Uses
- Lapidary, Collector, Decorative
- Host rock
- sedimentary basins
- Organism
- Ooids (spherical grains of concentric layers), not an organism
- Preservation
- Silica replaces the original carbonate by the same volume
Where rockhounds find silicified oolite
2 mapped spotsClassic worldwide localities
- Pennsylvania, USA
- Utah, USA
- France
- United Kingdom
Field-hunting tip
Where it forms: sedimentary basins. If you start seeing quartz, calcite, dolomite in float, you are in the right ground. In the U.S., the densest reported localities are in Georgia. Start trip planning there.
More silicified oolite photos
Common questions
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Find silicified oolite on the map
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