Once a Week, Ordinary Folks Get to Search for One of the World's Rarest Gems

March 3, 2022

Halfway between Los Angeles and San Francisco near the headwaters of the San Benito River, amateur treasure hunters pay $100 per ticket for the thrill of scouring the screening field at the Benitoite Mining Company for one of the world’s rarest gemstones — the beautiful bright blue benitoite.

From 9am to 3pm on Saturdays, the regular mining operations give way to a stream of rockhounds looking for a relaxing day of outdoor family fun — and the possibility of striking it rich. The mining company's website notes that there is a 1 in 20 chance that a visitor will walk away with a stone of value. The ticket price is $50 for kids 12 and under.

Pronounced "ben-ee-toe-ite," the gem was discovered in 1907 by a prospector named James M. Couch, who originally believed be may have discovered a new source of sapphire due to the similar color. In 1909, a sample was sent to mineralogist Dr. George D. Louderback of the University of California, Berkeley, who concluded that blue stone was a previously unknown mineral.

It was named benitoite to honor its connection to the San Benito River in San Benito County, CA. While benitoite occurs in a number of locations globally — such as Montana, Arkansas, Japan and Australia — the Benitoite Mining Company in Coalinga, CA, remains the primary source for gem-quality crystals.

In 1985, benitoite became California's official state gemstone.

The Benitoite Mining Company limits the amount of booty that each prospector may take home. Whatever fits in a quart-size bag can be kept. Larger specimens are priced individually. The actual mine is not open to the public due to safety concerns, but material from the mine is delivered to the screening area, where visitors are provided with digging tools. Reservations are required.

Officially, benitoite is a rare blue barium cyclosilicate found embedded in hydrothermally altered serpentinite. Sometimes referred to as the "blue diamond," benitoite ranges in hue from light transparent to dark blue. Medium-dark stones command the highest prices. The gem scores a 6 - 6.5 on the Mohs hardness scale. By comparison, sapphire rates a 9 and diamond rates a 10.

Credits: Images by Didier Descouens, CC BY-SA 4.0, via Wikimedia Commons.