sedimentary
Tufa
Calcareous Tufa (CaCO3)
Hardness: 3 (Mohs scale), Color: tan, cream, or grayish-brown, Luster: dull to earthy, Crystal Structure: trigonal (microcrystalline calcite), Cleavage: none, Specific Gravity: 1.5 - 2.5 (highly variable due to porosity)
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Physical properties
Hardness: 3 (Mohs scale), Color: tan, cream, or grayish-brown, Luster: dull to earthy, Crystal Structure: trigonal (microcrystalline calcite), Cleavage: none, Specific Gravity: 1.5 - 2.5 (highly variable due to porosity)
Formation & geological history
Formed by the chemical precipitation of calcium carbonate from ambient temperature surface or ground waters, often in alkaline lakes, geothermal springs, or areas with significant evaporation.
Uses & applications
Used primarily in landscaping, aquarium decoration (as it helps buffer pH), and historical construction in regions where it is abundant.
Geological facts
The Mono Lake tufa towers in California are some of the most famous examples. Tufa is often confused with travertine, but tufa is typically more porous and forms in cooler water than travertine.
Field identification & locations
Identify in the field by its highly porous, sponge-like or honeycomb texture and its reaction (fizzing) when exposed to a weak acid like vinegar. Commonly found near rift lakes or limestone springs.
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