Rhyolite: Laf124

Title: Rhyolite: Laf124
Description: Hand Sample: This is rock contains many small to medium sized diverse crystal with a brick-colored groundmass. 40% of the crystals are white plagioclase, 5%-10% of them are pink alkali feldspar,20% of them are quartz (most of them are medium sized), and 5% of the them are black augite (most of them are in very small pieces).

Thin Section: From the thin section we can see a vitrophyric texture. The felty groundmass is consisted of mostly volcanic glass.There are mainly two kinds of phenocrysts. One of them is a xenolith(a).The other type of phenocrysts are equigranular ang also have an embayed texture(b). The phenocrysts (1) are mostly(95%) quartz, because they have a low birefringence color and some display undulatory extinction. (2) maybe a hematite, because of its reddish color in both PPL and XPL. There is only one hematite crystal in this thin section. because it has a very high relief and displays parallel extinction. There are also some(1%-2%) hornblende inclusion in in the quartz phenocryst(3).

Life History: This rock cooled slowly undergroud for a while, then it was brought to a new compositional environment, which is why the crystal are dissolving.

Location: Unknown
Creator: 8585
Mediator: Tamara Carley

Media: https://exhibits.lafayette.edu/geology/files/original/1fbfdd9ff516b3117ad81b970a5d9a29.JPG; https://exhibits.lafayette.edu/geology/files/original/f2ae5659a8ac54e2b4c7bfd03e1ba2f8.JPG; https://exhibits.lafayette.edu/geology/files/original/482ca3a866b7e37162770b71b66c6e21.JPG; https://exhibits.lafayette.edu/geology/files/original/9e4d6806db9a97c71aaca870e326faf4.JPG; https://exhibits.lafayette.edu/geology/files/original/f0669abf54032288937f77cf17a72821.JPG; https://exhibits.lafayette.edu/geology/files/original/ded7a0acf2948367425215b4bcad734e.JPG

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