23g / 40mm Herkimer Diamond, excellent clarity, moving carbon and quicksand Herkimer diamonds rank between 7 and 7.5 on the Mohs hardness scale. This is softer than a diamond, which scores 10 on the scale. Herkimer diamonds are actually quartz crystals that are named after Herkimer County, New York, where they were first discovered. They are known for their high luster and are often faceted into 18 natural facets. Here are some things to consider about Herkimer diamonds: Inclusions Many Herkimer diamonds have black spots or bubbles caused by inclusions of black carbon, oil, water, or liquid petroleum. More valuable Herkimer diamonds are clear and free of inclusions. Handling Herkimer diamonds can chip or crack, so they should be handled gently and protected from hard knocks, pressure, and other hard stones and metals. Rarity Herkimer diamonds are more rare than common diamonds and are over 500 million years old.