sedimentary

Calcareous Tufa / Limestone Fragment

Calcium Carbonate (CaCO3)

Hardness: 3 (Mohs scale), Color: White to earthy tan/beige, Luster: Dull or earthy, Crystal structure: Hexagonal (Trigonal) as microcrystalline calcite, Cleavage: Perfect rhombohedral (though rarely visible in earthy specimens), Specific Gravity: 2.71

Identified June 2, 2026More sedimentary →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed by the precipitation of carbonate minerals from ambient temperature water bodies, hot springs, or lake beds. Often results from the removal of CO2 by plants or algae, triggering chemical precipitation of calcium carbonate over time.

Uses & applications

Mainly used as a decorative stone in gardens, aquariums, and landscaping. Historically used for lightweight construction in some regions due to its porous nature. High-purity limestone is used in cement production and chemical industries.

Geological facts

Tufa is often confused with Travertine; however, Tufa is formed at ambient temperatures while Travertine forms at geothermal hot springs. Tufa can often trap plant fossils or organic matter within its structure.

Field identification & locations

Identify in the field by its porous, brittle texture and its violent effervescence (bubbling) when a drop of diluted hydrochloric acid is applied. It is commonly found near alkaline lakes and karst springs.

Other sedimentary specimens

See all

Sandstone or Siltstone

Arenite (if sandstone)

Sedimentary

Sandstone

Arenite (primarily SiO2)

sedimentary

Sandstone Grain

Clastic Sedimentary Rock Grain (SiO2 dominated)

sedimentary

Chert Breccia

Brecciated Chert (Microcrystalline Silica)

sedimentary

Shale or Slaty Mudstone

Argillaceous sedimentary rock

sedimentary

Sandstone

Arenite

sedimentary