Tufa

Physical Properties

Hardness: 3-4 (Mohs); Color: Tan, beige, grey, or creamy white; Luster: Dull to earthy; Structure: Highly porous, vesicular, or sponge-like; Cleavage: None (amorphous/microcrystalline); Specific Gravity: Low due to porosity.

Formation & Geological History

Formed by the precipitation of carbonate minerals out of ambient temperature water (freshwater). This usually occurs at the mouths of freshwater springs, along lake shores, or in areas with alkaline water. Unlike travertine, it is not formed from thermal springs.

Uses & Applications

Historically used as a lightweight building material in ancient architecture; currently used in landscaping (rock gardens) because its porosity allows plants to take root, and in aquariums for pH buffering.

Geological Facts

Tufa is so porous that it can sometimes feel surprisingly light for its size. It often contains impressions of plants, twigs, or moss that were present when the minerals precipitated around them.

Field Identification & Locations

Identify by its 'spongy' or 'swiss-cheese' appearance and its reaction (fizzing) when a small drop of vinegar or weak acid is applied, indicating calcium carbonate. Commonly found in Mono Lake (California) or around karst landscapes.

Identified on: 4/22/2026

Mode: Standard