VOLCANIC GEMS

STORY AND PHOTOS BY BILL ROZDAY

I found it lying in the middle of a dirt road among vast vineyards near Cobb Mountain, overlooking Clearlake, California. It looked precisely like a piece of broken glass from an amber beer bottle, but multi-milliondollar vineyards that make glass litter seems unlikely. I also knew that the road crossed the epicenter of Lake County diamond country.

The specimen I found was a xenolith, formed from molten silicon dioxide contacting a coloring element, somewhat as a glassblower fashioning decorative glass. The high-temperature environment within the magma chamber of Mount Konocti, 1,112 degrees at a minimum, gave it a 7.5 or higher Mohs hardness and allowed absorption of the coloring element. The resulting “diamond” was not merely stained quartz but a gem. Many thousands of years after its origin in a volcanic eruption, the road grader bit deeper into the earth and uncovered it.