Name: Garnet Gneiss
Type: rock
Class: Metamorphic
Subclass: Gneis
Particle Size: Fine
Sample No.: gneiss2
Owner: JHU
Wavelength Range: All
Origin: Sample No. 466, The Hunt and Salisbury Collection at the U.S.Geological Survey, Denver, Co.
Collection Date: N/A
Description: This is a very coarse-grained rock composed of porphyroblasts of garnet frequently enclosing embayed remnants of tectosilicates and opaques.  Larger grains of heavily altered alkali feldspar (oligoclase and K-spar) and quartz make up the bulk of the remainder of this rock.Particle size was 0-75 Micrometer. Original ASTER Spectral Library name was jhu.becknic.rock.metamorphic.gneiss.fine.gneiss2.spectrum.txt
The garnet crystals are rimmed with sillimanite and opaques (magnetite?), and 
occasionally with chlorite instead.  The chlorite, usually associated with 
pyrophyllite, are also very common as alteration products along fractures and 
around sillimanite grains.  Biotite occurs throughout the section, while one 
quartz(?) grain was heavily rutilated.  There was 42% garnet, 16.6% feldspar, 
13.2% quartz, 9.6% sericite & alterations, 7.5% chlorite, 3.7% pyrophyllite, 3.4% 
sillimanite, 3.2% opaques, and 0.8% biotite. 
