mineral
Pale green mineral specimen, likely prehnite or green calcite
Tentatively prehnite, Ca₂Al(AlSi₃O₁₀)(OH)₂; visual identification is uncertain from the photograph
AI-generated identification · may be incorrectPale mint-green, dull to pearly luster, botryoidal/granular texture, and no clearly visible crystal faces. Prehnite has Mohs hardness 6–6.5, while calcite is softer at 3 and effervesces in dilute acid.
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Physical properties
Pale mint-green, dull to pearly luster, botryoidal/granular texture, and no clearly visible crystal faces. Prehnite has Mohs hardness 6–6.5, while calcite is softer at 3 and effervesces in dilute acid.
Formation & geological history
Prehnite forms in cavities and fractures of basaltic volcanic rocks through low-temperature hydrothermal alteration; calcite commonly forms in veins and cavities. Such minerals range from ancient to modern geological settings.
Uses & applications
Small specimens are primarily collector items; attractive prehnite may be cabochon-cut, while calcite is widely used industrially but this tiny piece has no practical commercial use.
Geological facts
The rounded, pale-green appearance is consistent with botryoidal prehnite, though lighting and scale prevent confident determination. A hardness and acid test would distinguish the main alternatives.
Field identification & locations
Common sources include India, Australia, South Africa, China, and the United States for prehnite; calcite is worldwide. Test an inconspicuous area: calcite scratches easily with a steel pin and fizzes in acid, whereas prehnite generally does neither.
