Banded Calcite or Travertine

Hardness: 3 (Mohs scale); Color: Typically white, cream, tan, brown, or yellowish, often with distinct banding; Luster: Vitreous to dull; Crystal structure: Trigonal/Rhombohedral, but often massive or fibrous; Cleavage: Perfect rhombohedral cleavage (not always obvious in massive forms); Specific Gravity: 2.71

Formed by the precipitation of calcium carbonate from mineral-rich waters. Travertine specifically forms in hot springs, geysers, or caves when carbon dioxide outgasses from groundwater, causing calcite to deposit. The banding often results from variations in mineral content or water flow over time. Geological age can vary widely, from relatively recent (thousands of years) to much older formations (millions of years).

Widely used as an ornamental stone in construction for flooring, wall cladding, countertops, and decorative objects. It can be polished to a high luster. Historically, it has been used for sculptures and building materials (e.g., the Colosseum in Rome). Not typically used in jewelry due to its relative softness.

Many famous historical buildings and natural formations are made of or contain travertine, including the Roman Colosseum and the hot spring terraces of Pamukkale, Turkey, and Yellowstone National Park. The banded appearance is often quite beautiful and sought after.

In the field, look for its distinctive banding and often porous or fibrous texture. It will fizz vigorously when a drop of dilute hydrochloric acid is applied (indicating carbonate). Its relative softness means it can be scratched with a knife or a copper penny. Common locations include areas with hot springs, caves (where it forms stalactites and stalagmites), and ancient lake beds. It's often found in arid and semi-arid regions. Collectors often seek specimens with well-defined, attractive banding.