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Felsites in the Fiddle Creek Schist

View on map:45.492209°N 116.312634°W

Comments

The rock is a "fine-grained, pyrite-bearing quartzofeldspathic schist with abundant quartz porphyroclasts".  The schist fabric wraps pyrite crystals locally.  Stop 7 in Schmidt et al. 

Description


Felsite

Felsite (also called felstone [1]) is a very fine grained volcanic rock that may or may not contain larger crystals. Felsite is a field term for a light colored rock that typically requires petrographic examination or chemical analysis for more precise definition. Color is generally white through light gray, or red to tan and may include any color except dark gray, green or black (the colors of trap rock). The mass of the rock consists of a fine-grained matrix of felsic materials, particularly quartz, sodium and potassium feldspar, and may be termed a quartz felsite or quartz porphyry if the quartz phenocrysts are present. This rock is typically of extrusive origin, formed by compaction of fine volcanic ash, and may be found in association with obsidian and rhyolite. In some cases, it is sufficiently fine-grained for use in making stone tools. Its fine texture and felsic components allow for good knapped pieces, much like working chert, producing conchoidal fracture.

References

  • http://en.wikipedia.org/wiki/Felsite
  • Page 192 - Schmidt, K. L., et al., 2016, Mesozoic tectonics west of the accretionary boundary in west-central Idaho: A road log along U.S. Highway 95 between Moscow and New Meadows, Idaho: Geol. Soc. Am., Field Guide 41, p. 175-209.
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