USGS SAN JUAN MOUNTAINS MELASYENITE, Unusual Igneous Rocks GEOCHEM PETROLOGY

Description

ODDBALL ROCKS!!!!  ONLY ONE AVAILABLE!!
This is USGS Bulletin 11311-C,
Precambrian Melasyenite of Ute Creek, San Juan Mountains, Colorado - Chemistry, Petrology and Strontium Isotopes
. This 15-page book is a neat little study of some interesting rocks in the San Juan mountains.
Melasyenite is an odd igneous rock mostly lacking quartz but containing a lot of feldspar. Usually there are not that many dark minerals, but this one has quite a lot - enough to get the prefix mela, which means dark. It is about half dark minerals like hornblende and biotite. This study gave the rocks a good look in a few different ways, examining the chemistry, petrology (mineral composition) and isotopes, to get a little better picture of the thing. Kind of a cool study of a weird rock. It might be worth a hike to have a look at it and bring back a chunk or two. The map has enough information to get you there, and the thing is big enough not to miss, being over 3x1 miles in size.
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