sedimentary
Oolitic Limestone
Oolite (Sedimentary rock composed of CaCO3)
Hardness: 3-4 on Mohs scale; Color: Cream, tan, or white with reddish-brown staining; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Composition: Primarily calcite with iron oxide impurities.
- Hardness
- 3-4 on Mohs scale
- Color
- Cream, tan, or white with reddish-brown staining
- Luster
- Dull to earthy
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Physical properties
Hardness: 3-4 on Mohs scale; Color: Cream, tan, or white with reddish-brown staining; Luster: Dull to earthy; Crystal structure: Trigonal (microcrystalline); Composition: Primarily calcite with iron oxide impurities.
Formation & geological history
Formed in warm, shallow, agitated marine environments where calcium carbonate precipitates around a grain of sand or shell fragment (nucleus). The constant rolling in waves creates the spherical 'ooids'. This specimen shows Liesegang rings (reddish bands) from later mineral-rich fluid seepage.
Uses & applications
Used widely in construction (Portland stone), as a soil conditioner (lime), and as a flux in steel making. Higher quality specimens are used for architectural masonry and sculpture.
Geological facts
The term 'oolite' comes from the Greek word 'oion' meaning egg, because it looks like fish roe. Much of the famous architecture in Bath and London, England, is built using oolitic limestone.
Field identification & locations
Identify in the field by looking for tiny (0.25–2.0 mm) spherical grains; it will effervesce (fizz) vigorously when in contact with dilute hydrochloric acid. Commonly found in tropical marine shelf areas.
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