What Is Herkimer Diamond? - Geology In

Key Characteristics of Herkimer Diamonds

Double Termination: Unlike typical quartz crystals, which grow with a single point, Herkimer diamonds naturally form with points on both ends, giving them a "double-terminated" structure. This happens because they grow in pockets of dolostone (a type of sedimentary rock) where they are free to develop points on both sides without attachment to a host rock.

Exceptional Clarity and Sparkle: Herkimer diamonds are known for their clarity, often being exceptionally clear and transparent, with a glassy, diamond-like sparkle. They are sometimes almost water-clear but can also contain small inclusions, air bubbles, or black carbon deposits, which add character to each stone.

Natural Faceting: Herkimer diamonds often form with 18 natural facets and are already well-shaped when they are mined, which reduces the need for cutting and polishing compared to other crystals.

Composition: Despite their name, Herkimer diamonds are not carbon-based diamonds. They are made of silicon dioxide (SiO₂), the same as regular quartz. Their “diamond” name comes from their clarity, brilliance, and naturally occurring crystal form, which resembles cut gemstones.

Size and Rarity: Herkimer diamonds are typically small, with most crystals being under an inch long. Larger, high-clarity Herkimers are rare and highly valued by collectors and jewelry makers.

Colors: Herkimer diamonds can be found in a variety of colors, including clear, white, brown, and black.

Herkimer Diamonds

Inclusion: A fluid inclusion is a pocket within a crystal containing liquid, usually water, sometimes also methane or oil, and rarely, smaller crystals. A phantom is a crystal containing other visible crystals of the same type, a skeletal crystal contains a series of crystal edge outlines inside the crystal and a hopper crystal has its faces replaced by a step like pattern.

Herkimer Diamond. Photo: Northern Maine Minerals

Where to find Herkimer Diamonds

Herkimer diamonds are a popular tourist attraction in upstate New York. There are several commercial mines where visitors can dig for their own diamonds. Herkimer diamonds are also available from many rock and gem shops around the world.

Herkimer Diamond Mine, Herkimer county, New York

The undisputed king of New York gem digging, this iconic location is famous for its "diamonds" (double-terminated quartz crystals). They offer public and private digging areas, with beginner-friendly instruction, guided tours, and even educational exhibits.

Their website provides detailed information, pricing, and even a virtual tour: Herkimer Diamond Mines

Address: 4626 State Route 28 North Herkimer, NY 13350

Grove Diamond Mine, St. Johnsville, New York