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Tuff of St. Gertrude

View on map:46.023300°N 116.402700°W

Comments

The outcrop here consists of a welded tuff with compacted pumice fragments and plagioclase and quartz crystals as phenocrysts.  The composition is rhyolite (78% SiO2).  The tuff dates to 199 Ma plus or minus 8 Ma.  Stop 2 in Schmidt et al.

Description


Tuff

Tuff (from the Italian tufo) is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is compacted into a solid rock in a process called consolidation. Tuff is sometimes called tufa, particularly when used as construction material, although tufa also refers to a quite different rock. Rock that contains greater than 50% tuff is considered tuffaceous.

References

  • http://en.wikipedia.org/wiki/Tuff
  • Page 186 - 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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