mineral

Polished banded calcite (onyx marble) heart

Banded calcite, predominantly CaCO₃; commonly marketed as “honey onyx” or “Mexican onyx”

AI-generated identification · may be incorrect

Hardness 3 on the Mohs scale; cream, tan, brown, and gray bands with a waxy-to-glassy polished luster. Calcite is trigonal, has perfect rhombohedral cleavage, and fizzes with dilute hydrochloric acid; specific gravity is about 2.7.

Identified August 31, 2026More mineral →

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At a glance

Common name: Polished banded calcite (onyx marble) heart
Scientific name: Banded calcite, predominantly CaCO₃; commonly marketed as “honey onyx” or “Mexican onyx”
Category: mineral
Identified: August 31, 2026
Method: Standard

AI Estimated Value

Approximately $10–$40 for a palm-sized polished heart; $50–$150+ for unusually large, translucent, or exceptionally patterned pieces.

Not an official valuation

AI estimate for general interest only — not an appraisal. Actual value depends on condition, provenance, and market demand. Verify with a professional before buying, selling, or insuring.

This identification was generated by AI and may contain errors. Verify important details before relying on them — and never use an AI result to judge whether a specimen is safe to handle. Read the full disclaimer

Physical properties

Formation & geological history

Forms when carbonate-rich groundwater deposits layers of calcite in caves, springs, or fractures; the banding records changing impurities and flow conditions. Most commercial material formed in relatively young Cenozoic deposits, though age depends on locality.

Uses & applications

Carved ornaments, hearts, bookends, decorative slabs, and interior surfaces; softer than quartz and unsuitable for heavy-wear flooring. Modest collector and gift-shop value.

Geological facts

Despite the trade name “onyx,” this is calcite, not quartz chalcedony. Stronger translucency and acid effervescence distinguish it from true quartz onyx.

Field identification & locations

Identify by parallel curved bands, low hardness, rhombohedral cleavage, and acid reaction; common sources include Mexico, Pakistan, Turkey, and Argentina. Avoid scratching or prolonged acids.