Tumbled pink calcite (probable)

The specimens appear to be small, rounded, polished or naturally smoothed pieces with a pale peach-to-pink color and cream/tan patches. Calcite has Mohs hardness 3, vitreous to pearly or waxy luster, rhombohedral crystal structure, excellent rhombohedral cleavage, and specific gravity about 2.71. The color may result from trace manganese or iron. The image is not sufficient for a certain identification; pink opal, aragonite, or dyed chalcedony are possible alternatives.

Calcite forms in sedimentary limestone and marble, hydrothermal veins, caves, and mineral-rich cavities. Pink manganocalcite commonly forms from hydrothermal fluids or alteration of carbonate rocks. Calcite deposits range from Precambrian to recent age, so the age of an individual piece cannot be determined from appearance alone.

As a mineral, calcite is used in cement, lime, construction aggregate, agricultural soil treatment, chemical processing, and optical applications. Attractive pink pieces are sold as inexpensive polished specimens, ornaments, or metaphysical stones rather than as high-value gemstones.

Calcite reacts strongly with dilute hydrochloric acid, producing visible fizzing; vinegar may produce a slower reaction. It is much softer than quartz and can be scratched by a steel knife or copper coin. The rounded shape indicates tumbling, water wear, or both, so the original crystal form and cleavage are no longer visible.

Common sources of pink calcite and manganocalcite include Mexico, Peru, Argentina, Romania, and parts of the United States. Field identification should be confirmed with a hardness test on an inconspicuous area and an acid test, preferably on a freshly exposed surface. If it does not fizz and resists scratching, pink opal or chalcedony becomes more likely. The pictured pieces may also be polished pink opal, which cannot be excluded from this photograph alone.