Limestone (specifically Travertine or Tufa)

Physical Properties

Hardness: 3 on Mohs scale; Color: Tan, brown, white, and reddish-orange due to iron oxides; Luster: Dull to earthy; Crystal Structure: Trigonal (microcrystalline); Cleavage: None (conchoidal fracture when dense); Porous texture.

Formation & Geological History

Formed by the precipitation of carbonate minerals from solution in ground and surface waters, or in poorly oxygenated geothermal springs. This specific specimen shows weathering and iron staining likely from terrestrial exposure.

Uses & Applications

Used widely in construction as building stone, aggregate for concrete, production of cement, and in agriculture as soil conditioner.

Geological Facts

Limestone makes up about 10% of the total volume of all sedimentary rocks. It is the primary storage rock for petroleum and natural gas in many parts of the world.

Field Identification & Locations

Identify in the field by its reaction to dilute hydrochloric acid (it will fizz/effervesce). Often contains terrestrial or aquatic fossils depending on the specific deposit. Common in karst landscapes.

Identified on: 4/20/2026

Mode: Standard