sedimentary
Tufa
Calcareous Tufa (CaCO3)
Hardness: 3-4 (Mohs); Color: Tan, beige, or grey with dark manganese staining; Luster: Dull/Earthy; Crystal Structure: Microcrystalline calcite; Cleavage: None; Specific Gravity: Low (highly porous/vesicular).
- Hardness
- 3-4 (Mohs)
- Color
- Tan, beige, or grey with dark manganese staining
- Luster
- Dull/Earthy
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Physical properties
Hardness: 3-4 (Mohs); Color: Tan, beige, or grey with dark manganese staining; Luster: Dull/Earthy; Crystal Structure: Microcrystalline calcite; Cleavage: None; Specific Gravity: Low (highly porous/vesicular).
Formation & geological history
Formed through the chemical precipitation of calcium carbonate from ambient-temperature water, typically in freshwater springs, lake shores, or areas with high alkaline content. It accumulates over years to millennia.
Uses & applications
Used primarily in decorative landscaping (rock gardens), as an aquarium substrate due to its buffering capacity, and historically in some lightweight masonry construction.
Geological facts
Tufa often captures biological materials like leaves or twigs during formation, leaving behind detailed casts or impressions. Unlike Travertine, Tufa is highly porous and lacks high-pressure hydrothermal origins.
Field identification & locations
Identify in the field by its sponge-like, porous appearance and 'fizzy' reaction to dilute hydrochloric acid. Common in the Great Basin (e.g., Mono Lake) and limestone-rich spring environments.
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