While continuing through Owens Valley, another interesting geological feature reveals itself to us. This protrusion is known as Knopf’s Knob.
Knopf’s Knob is a unique exposure of columnar granite, which contains Pleistocene olivine basalt. The basalt contains many xenoliths of quartz monzonite, which is especially interesting.
A xenolith, explained, is any rock fragment that becomes enveloped in another rock fragment during the latter’s formation. The basaltic intrusion here has quartz xenoliths and has even formed glass during its formation. This crystal glass is formed at a temperature of roughly 1,100° C, which is toasty! Xenoliths are typically formed with magma eruption, indicating that this area is volcanically active.
To be considered a true xenolith, the surrounded rock/mineral must be identifiably different than the rock which surrounds it. Any rock surrounded by rock of a similar type is called an autolith. This mainly happens when magma picks up and engulfs an already solidified piece of that same magma from an earlier eruption.
**Notice: Please, if you are so inclined to collect samples of the glass, there are numerous fragments in the rubble at the base of the hill. Do not collect from the bedrock outcrops. However, do respect nature and keep in mind that if everyone collected samples of the glass, there would be none left! **
To log this Earthcache, please complete the following:
1) send a message to me with these questions answered:
-What is the name of this Earthcache?
-How many people are in your group?
-Looking at Knopf’s Knob, would you identify the different looking rock intrusions as xenoliths or autnoliths?
-What other features of this isolated outcropping indicates that this area is volcanically active?
2) Post a picture of you, your squad, or your GPS with the Knob in the background! This is more of a recommendation, as I understand some people do not own cell phones or cameras.
Sources:
-http://www.muststayawake.com/guide12_files/guide12_P09.htm
-https://www.sandatlas.org/olivine-basalt-from-oahu/
-https://en.wikipedia.org/wiki/Xenolith
