mineral

Polished green calcite (often sold as “onyx marble”)

Calcite, CaCO₃; banded crystalline limestone/travertine

AI-generated identification · may be incorrect

Typically pale to vivid green with translucent, wavy bands and vitreous to silky luster; Mohs hardness 3, rhombohedral cleavage, white streak, specific gravity about 2.7. The slab appears polished and may be dyed or surface-treated.

Identified August 25, 2026More mineral →

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Physical properties

Formation & geological history

Forms when calcium-carbonate-rich groundwater precipitates in caves, springs, or cavities, producing layered travertine or banded calcite; deposits are generally geologically young to ancient depending on locality.

Uses & applications

Used for ornamental slabs, carvings, paperweights, and inexpensive cabochons; too soft and acid-sensitive for demanding jewelry or heavy construction. Avoid vinegar and abrasive cleaning.

Geological facts

Commercial “green onyx” is usually not true onyx (chalcedony); it is commonly banded calcite or aragonite marble. Calcite effervesces visibly with dilute hydrochloric acid.

Field identification & locations

Identify by softness, rhombohedral cleavage, pale streak, and strong reaction to dilute acid; common sources include Mexico, Pakistan, Turkey, and South America. A knife may scratch it, though polished surfaces can resist lightly.