sedimentary
Oolitic Limestone (Egg Stone)
Oolite (Chemical sedimentary rock, primarily CaCO3)
Hardness: 3-4 on Mohs scale; Color: typically off-white, cream, or light grey; Luster: dull to earthy; Structure: composed of many small spheres called ooids (0.25 to 2 mm diameter); Specific Gravity: 2.5-2.7.
- Hardness
- 3-4 on Mohs scale
- Color
- typically off-white, cream, or light grey
- Luster
- dull to earthy
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Physical properties
Hardness: 3-4 on Mohs scale; Color: typically off-white, cream, or light grey; Luster: dull to earthy; Structure: composed of many small spheres called ooids (0.25 to 2 mm diameter); Specific Gravity: 2.5-2.7.
Formation & geological history
Formed in warm, shallow, supersaturated marine waters. Calcium carbonate precipitates around a nucleus (like a grain of sand or shell fragment) and is rolled by wave action, creating concentric layers. These specimens typically range from the Jurassic to Carboniferous periods.
Uses & applications
Used as a high-quality building stone (e.g., Portland stone), in the manufacture of lime and cement, and occasionally as a decorative garden stone or aquarium substrate.
Geological facts
The word 'oolite' comes from the Greek word 'oion' for egg, referring to its resemblance to fish roe. Much of the architecture in the Cotswolds (UK) and Indiana (USA) is built from this specific rock type.
Field identification & locations
Identify in the field by its distinct 'sandpaper' texture and the presence of tiny, seed-like round grains visible under a hand lens. It will react and fizz strongly when exposed to dilute hydrochloric acid (vinegar may cause a weak reaction).
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