sedimentary
Tufa (Limestone)
Calcareous Tufa (CaCO3)
Hardness: 3-4 (Mohs scale), Color: Cream, tan, or grey, Luster: Dull/Earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: None/Irregular, Specific Gravity: 1.5 - 2.3 (low due to porosity)
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Physical properties
Hardness: 3-4 (Mohs scale), Color: Cream, tan, or grey, Luster: Dull/Earthy, Crystal Structure: Trigonal (microcrystalline), Cleavage: None/Irregular, Specific Gravity: 1.5 - 2.3 (low due to porosity)
Formation & geological history
Formed by the precipitation of carbonate minerals from ambient temperature water bodies, such as hot springs, lake shores, or areas with high calcium carbonate concentrations. Often associated with the Holocene or Pleistocene epochs.
Uses & applications
Used in landscaping, high-end aquarium decoration (base rock), architectural veneers, and historically as a lightweight building stone in specific regions.
Geological facts
Tufa is highly porous and often contains imprints or organic remnants of plants, moss, or shells that were trapped during the rapid mineral precipitation. It is different from Travertine, which forms in geothermal hot springs.
Field identification & locations
Identify in the field by its sponge-like, porous texture and reaction (fizzing) to dilute hydrochloric acid. Commonly found in Mono Lake (California), the Great Basin, and limestone-rich karst regions. For collectors, look for unique branching shapes.
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