mineral

Black Agate

Chalcedony (SiO2)

Hardness of 6.5 to 7 on the Mohs scale, predominantly black color with occasional white or gray translucent banding, waxy to vitreous luster, microcrystalline/cryptocrystalline quartz structure, conchoidal fracture with no true cleavage, and a specific gravity of 2.60 to 2.65.

Identified July 30, 2026More mineral →

Explore Black Agate in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Forms primarily in the cavities of volcanic and metamorphic rocks through the deposition of silica-rich groundwater solutions in concentric layers over long geological periods.

Uses & applications

Commonly used for tumbled stones, beads, jewelry, carvings, and ornamental objects.

Geological facts

Natural black agate is relatively rare in nature, and much of the black agate sold commercially is actually gray or brown chalcedony that has been artificially treated or dyed to achieve its deep black color.

Field identification & locations

Identified by its waxy luster, smooth tumbled feel, hardness capable of scratching glass, and microcrystalline structure. Often found in river gravels, glacial drift, and volcanic regions worldwide.