mineral

Banded agate tower (likely onyx/chalcedony)

Microcrystalline quartz, SiO₂; commonly called banded agate or black-and-white onyx

AI-generated identification · may be incorrect

Hardness ~6.5–7 Mohs; vitreous to waxy luster, translucent gray-white bands with a dark brown-black central zone, and no visible cleavage. The polished hexagonal point is a human-shaped geological specimen; dark coloration may be natural or enhanced.

Identified August 17, 2026More mineral →

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At a glance

Common name: Banded agate tower (likely onyx/chalcedony)
Scientific name: Microcrystalline quartz, SiO₂; commonly called banded agate or black-and-white onyx
Category: mineral
Identified: August 17, 2026
Method: Standard

AI Estimated Value

Approximately $15–$60 for a common polished tower; $75–$200+ for large, sharply banded, naturally colored, or high-quality specimens.

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 silica-rich groundwater fills cavities in volcanic rock, depositing chalcedony and quartz in successive bands. Agate formation commonly occurred during the Cenozoic and older volcanic episodes, depending on locality.

Uses & applications

Used for carvings, cabochons, ornamental towers, bookends, and jewelry; usually decorative rather than industrial.

Geological facts

Agate is a variety of chalcedony distinguished by banding; “onyx” is often used commercially for straight-banded black-and-white material, even when it is technically agate.

Field identification & locations

Identify by concentric or planar microcrystalline-quartz bands, glassy polish, lack of cleavage, and hardness sufficient to scratch ordinary glass. Common sources include Brazil, Uruguay, Mexico, India, and Madagascar.