mineral

Herkimer Diamond

Double-Terminated Quartz (SiO2)

Hardness: 7.5 (slightly harder than common quartz); Color: Transparent to Smokey; Luster: Vitreous; Crystal Structure: Hexagonal; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65.

Hardness: 7
Color: Transparent to Smokey
Luster: Vitreous

Identified March 25, 2026More mineral →

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Physical properties

Hardness: 7.5 (slightly harder than common quartz); Color: Transparent to Smokey; Luster: Vitreous; Crystal Structure: Hexagonal; Cleavage: None/Conchoidal fracture; Specific Gravity: 2.65.

Formation & geological history

Formed roughly 500 million years ago (Cambrian Period) in the Little Falls Dolostone through a slow hydrothermal process. These crystals grew in fluid-filled vugs or pockets with little or no contact with the host rock, allowing points to form on both ends.

Uses & applications

Predominantly used for mineral specimen collecting and jewelry. In higher-grade lapidary work, they are often used in their raw state to preserve their natural geometry.

Geological facts

They are not actually diamonds, which are carbon; they are quartz (silica). The name comes from their high refractive index and diamond-like clarity. They are famous for being 'doubly terminated,' meaning they naturally grow points on both ends without being cut.

Field identification & locations

Identify in the field by their distinct double points and occurrence within dolostone pockets. Found most famously in Herkimer County, New York, but similar double-terminated crystals appear in Pakistan and Tibet. Look for high clarity and internal rainbows or hydrocarbon inclusions (anthraxolite).