mineral

Pale green calcite or prehnite specimen

Calcite (CaCO₃), possibly prehnite [Ca₂Al₂Si₃O₁₀(OH)₂]

AI-generated identification · may be incorrect

Translucent pale green to gray-green, vitreous to pearly luster, with irregular cleavage and a roughly botryoidal or bladed form. Calcite has Mohs hardness 3 and rhombohedral crystals; prehnite is harder, about 6–6.5, and commonly forms rounded aggregates.

Identified August 13, 2026More mineral →

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Physical properties

Formation & geological history

Likely formed in hydrothermal veins or cavities in volcanic rock; calcite may be much younger than its host rock, while prehnite commonly forms during low-temperature alteration of basalt. Exact age and identity require testing.

Uses & applications

Primarily a collector specimen; calcite is used industrially for cement, lime, and aggregate, while prehnite is occasionally cut as a gemstone or cabochon.

Geological facts

A vinegar or dilute hydrochloric-acid test causes visible effervescence if it is calcite, but not prehnite. A hardness test and specific-gravity measurement would distinguish them more reliably.

Field identification & locations

Common sources include Mexico, Brazil, India, South Africa, and volcanic regions worldwide. The pale green color and translucent fibrous appearance suggest prehnite, but the image alone is insufficient for certainty.