sedimentary
Tufa
Calcareous Tufa (Calcium Carbonate, CaCO3)
Hardness: 3 on Mohs scale; Color: Cream, tan, or grey; Luster: Dull/Earthy; Structure: Highly porous, vesicular, or sponge-like structure with no visible crystals; Specific Gravity: Low due to porosity.
- Hardness
- 3 on Mohs scale
- Color
- Cream, tan, or grey
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3 on Mohs scale; Color: Cream, tan, or grey; Luster: Dull/Earthy; Structure: Highly porous, vesicular, or sponge-like structure with no visible crystals; Specific Gravity: Low due to porosity.
Formation & geological history
Formed by the precipitation of carbonate minerals from ambient temperature water bodies, often around hot springs or lake shores. It is chemically precipitated rather than being formed from organic debris or extreme heat/pressure.
Uses & applications
Historically used as a building material in ancient architecture; currently used in landscaping, as an aquarium substrate to buffer pH, and as a lightweight aggregate in mortar.
Geological facts
Tufa is often confused with travertine, but tufa is much more porous and forms in cooler water. Famous tufa structures include the massive 'tufa towers' at Mono Lake, California.
Field identification & locations
Identify in the field by its sponge-like appearance and light weight. It will react and fizz (effervesce) if a weak acid like vinegar is applied. Commonly found in Great Basin areas and near limestone-rich spring water.
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