pitchstone - a silica rich volcanic glass - dramatic hand/display specimen with flow folding of trains of microscopic felsic crystals
Pitchstone is a volcanic glass similar to obsidian but which contains more water, often has a waxy appearance and has an irregular hackly fracture, not the smooth conchoidal fracture of obsidian. It forms from a silica-rich lava, often occurring as dikes and showing fluid flow structures.
This pitchstone formed the selvages of rhyolitic dikes. It has trains of microscopic felsic crystals that show that the flowage was turbulent and not smoothly parallel to the dike walls.
Collected in the Dublin Hills, Inyo County, California, approximately 3.5 miles WSW of the town of Shoshone.
Dramatic example, roughly 1 " thick. The pencil is 5" long, for scale.
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Cut flat on both sides. The edge shows the waxy surface characteristic of pitchstone.
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