The Diamonds that aren’t Diamonds

By Sara Kurth

Herkimer Diamonds – are they real diamonds? Sadly no. But that doesn’t make them any less interesting. “Herks” as they are sometimes called, are actually quartz. But not just any quartz. They are rock crystal quartz – the clearest form of quartz, featuring double terminated points and 18 natural facets. The term “double terminated” indicates that the crystal comes to a point on both sides, not just one, as is commonly associated with quartz crystals. This is not unique to Herkimers, but only those crystals found by the Mohawk River in Herkimer County, New York can be called Herkimer Diamonds. Herkimers are traditionally transparent and colorless, but occasionally inclusions, or minerals or other materials trapped during formation, can be found. Liquid saltwater and petroleum, gaseous carbon dioxide, even minerals such as dolomite or other Herkimers have been found included in a larger Herkimer diamond.

Quartz is the most common mineral on earth’s crust and can be found in every kind of rock. Herkimers are formed only in sedimentary rocks, specifically in dolostone and limestone. Nestled within these 500-million- year-old rocks, are porous vugs. Vugs are cavities inside a rock. Many have heard of geodes. All geodes are vugs, but not all vugs are geodes. To be a geode, the cavity must be mostly spherical. Vugs need not be spherical, as long as there is a cavity present. The cavity in which Herkimers formed were created by subterranean marine deposits that were filled with mineral-rich liquid. As the liquid underwent tectonic shifts, heat and pressure caused crystal growth. The added pressure resulted in a somewhat symmetrical growth of the quartz crystals, causing the double termination. Much like the formation of carbon diamonds, pressure is essential for the formation of symmetrical crystal growth. Unlike how quartz grows in geodes, these crystals were suspended within the vug, having very little interaction with the host rock. This floating crystal, along with the high temperature and pressure, is the reason these crystals grow into the double terminated crystals we see today.

Herkimers have long fascinated humans. As far back as the first peoples of Mohawk Valley, Herkimers were held in high esteem. They were used as amulets, made into tools, and used for trade. In fact, the Mohawk people referred to themselves as Kanyenkehaka or “The People of the Crystals.” The fascination with these stones has not waivered with the settlement of western New York. Today, “Pick Your Own” Herkimer digging areas surround the area of Herkimer, New York. You can even find and have your very own Herkimer engagement ring made!

On Saturday May 7th at 2 p.m., we are excited to have Elizabeth Thielen speak about her adventures rockhounding in her home state of New York and her fascination with the Herkimer Diamonds. This interactive lecture will include hands-on samples! Sign up online.