Grossular with Diopside

Unknown Owner

Lustrous crystals of grossular measuring to 0.5 cm are in size across the top of matrix with light green crystals of diopside. In good condition.The Crestmore Quarries, located in Riverside County, California, are world-renowned for their complex and diverse mineralogy resulting from high-grade contact metamorphism. Geologically, the site features a classic skarn deposit where Mesozoic quartz monzonite porphyry intruded into Paleozoic magnesium-rich limestones (the Sky Blue and Chino marbles), creating over 150 different mineral species, including the type localities for foshagite, riversideite, and crestmoreite. The quarries, primarily the Commercial and Wet Weather pits, were operated by the Riverside Portland Cement Company starting in 1907 to extract limestone for cement production. Underground mining transitioned to large-scale surface quarrying and continued through most of the 20th century, with significant operations winding down in the 1980s as the deposit was depleted and the surrounding area became increasingly urbanized. Today, while industrial activity has ceased, the locality remains a cornerstone of metamorphic petrology and a legendary destination for mineralogists due to its unique assemblage of rare calcium silicates.