dacite - large hand/display specimen of gray porphyritic dacite, a rock common in the Archean continents white gypsum sand from Lake

white gypsum sand from Lake Lucero

This sand was collected in 1994 from a tiny cove near South Point

which continues to operate the mine (photo) for lead and zinc

probable source of this sand is the Big Sur River

dacite - large hand/display specimen of gray porphyritic dacite, a rock common in the Archean continents white gypsum sand from LakeDacite was a common rock in the Archean continents, forming when hot young oceanic crust subducted beneath thick continental plates. As the hot oceanic plate subducted into the mantle, it partially melted, dewatered and became hydothermally altered, with the melt gaining quartz and sodium and forming a magma that differentiated and became even more sodium and silica rich as it rose. As it cooled near the surface, quartz (sodium silicate), plagioclase