metamorphic
Yellow Calcite (or Marble / Onyx Marble)
Calcite (CaCO3) in crystalline marble form
AI-generated identification · may be incorrectHardness 3 on the Mohs scale, vitreous to waxy luster, shades of honey-yellow, amber, and mottled white/brown, rhombohedral cleavage visible under micro-fracturing, specific gravity ~2.71.
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Physical properties
Hardness 3 on the Mohs scale, vitreous to waxy luster, shades of honey-yellow, amber, and mottled white/brown, rhombohedral cleavage visible under micro-fracturing, specific gravity ~2.71.
Formation & geological history
Formed either by metamorphism of limestone into crystalline marble or by low-temperature precipitation in hydrothermal or cave/hot-spring environments (often commercially termed 'onyx marble').
Uses & applications
Popular for ornamental carvings, polished eggs, spheres, decorative sculptures, and metaphysical/lapidary collections.
Geological facts
Despite often being commercially sold under the trade name 'onyx' or 'Mexican onyx', it is actually composed of calcium carbonate (calcite/aragonite) rather than true silicious onyx (chalcedony).
Field identification & locations
Identifiable by its softness (readily scratched by a copper penny or steel blade) and vigorous effervescence in dilute hydrochloric acid. Commonly sourced from Pakistan, Mexico, China, and Peru.
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