mineral

Herkimer Diamond

Quartz (Silicon Dioxide) - SiO2

Hardness: 7.5 (slightly harder than typical quartz); Color: Clear to smoky; Luster: Vitreous/Adamantine; Crystal structure: Double-terminated hexagonal prism; Cleavage: None (conchoidal fracture); Specific gravity: 2.65

Hardness: 7
Color: Clear to smoky
Luster: Vitreous/Adamantine

Identified July 19, 2026More mineral →

Explore Herkimer Diamond 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

Formed in vugs (cavities) within Little Falls Dolostone during the Cambrian period, roughly 500 million years ago. Hot hydro-thermal fluids dissolved holes in the host rock where crystals grew slowly, allowing for high clarity.

Uses & applications

Primarily used as a collector specimen, in metaphysical jewelry due to its natural shape, and as a semi-precious gemstone.

Geological facts

Herkimer Diamonds are not actually diamonds but are exceptionally clear, double-terminated quartz crystals. They were first discovered in large quantities in Herkimer County, New York, which remains the premier world locality.

Field identification & locations

Identify by its natural 18-faceted double-termination and extreme clarity. Most commonly found in Herkimer County, NY, by breaking open dolostone rocks or digging through pocket clay. Collectors look for 'water-clear' specimens with minimal carbon inclusions.