dacite - large hand/display specimen of gray porphyritic dacite, a rock common in the Archean continents Two views of the same

Two views of the same specimen

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

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

The brown in this calcite is entirely natural

dacite - large hand/display specimen of gray porphyritic dacite, a rock common in the Archean continents Two views of the sameDacite 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