Herkimer diamonds are not true diamonds; rather, they are a distinct variety of quartz. These unique crystals are renowned for their exceptional clarity and characteristic double-terminated points, which give them a sparkling, naturally faceted appearance. The term “diamond” in their name refers to this aesthetic resemblance, not to their chemical composition or geological origin, which differ significantly from genuine diamonds.
Understanding Herkimer Diamonds
Herkimer diamonds are crystals composed of silicon dioxide (SiO2), the same chemical makeup as all other quartz varieties. Their formation began approximately 500 million years ago, during the Cambrian period, within cavities known as vugs inside dolostone bedrock in Herkimer County, New York. Organic matter decomposition released gases and silica-rich fluids into these voids, allowing the quartz crystals to grow slowly and freely without attaching to the host rock.
This unhindered growth environment results in their signature appearance: naturally occurring double-terminated crystals with 18 facets, typically six on each pointed end and six around the central body. Herkimer diamonds are highly prized for their exceptional clarity, often appearing as transparent as water. While many are crystal clear, some may contain inclusions such as black hydrocarbons, water bubbles (enhydro), or air, which contribute to their individual character. On the Mohs scale of mineral hardness, Herkimer diamonds typically score between 7 and 7.5, making them durable with a vitreous, or glassy, luster.
Herkimer Diamond Compared to True Diamonds
Despite their name, Herkimer diamonds are fundamentally different from true diamonds. Chemically, Herkimer diamonds are silicon dioxide, while true diamonds consist solely of carbon atoms arranged in a distinct crystalline structure. This difference in composition and atomic arrangement leads to vastly different physical properties. True diamonds, being the hardest known natural material, register a perfect 10 on the Mohs hardness scale. Herkimer diamonds, at 7 to 7.5 Mohs, are considerably softer and can be scratched by genuine diamonds, as well as rubies, sapphires, and topaz.
Unlike true diamonds, which must be precisely cut and polished by humans to achieve their sparkle, Herkimer diamonds emerge from the earth already possessing their natural facets and double termination. True diamonds are generally much rarer and hold a significantly higher market value compared to the more abundant Herkimer quartz crystals.
Herkimer Diamond Compared to Other Quartz
While Herkimer diamonds are a type of quartz, they exhibit unique characteristics that distinguish them from more common quartz varieties like amethyst or citrine. The primary difference lies in their crystal habit: Herkimer diamonds are naturally double-terminated, meaning they have points at both ends. Most other quartz crystals typically form with only one termination or as massive, non-crystalline formations.
This distinctive double-terminated habit arises from their growth conditions within isolated pockets in the dolostone, allowing them to develop freely in all directions. This environment also contributes to their superior clarity and brilliance, which often surpasses that of other quartz types. Although double-terminated quartz crystals can be found in other global locations, only those specifically sourced from Herkimer County, New York, are officially classified as “Herkimer diamonds.”