Name: Augite-hypersthene Andesite
Type: rock
Class: Igneous
Subclass: Intermediate
Particle Size: Solid
Sample No.: Andesite_H1
Owner: JHU
Wavelength Range: All
Origin: Saipan, via Smithsonian (Cat. Number. NMNH 108982-135)
Collection Date: N/A
Description: The sample is about 4 x 3 cm, brown on the weathered surface and dark gray on fresh surfaces. It is porphyritic with the phenocrysts making up about 25-30% of the rock. The groundmass is gray and microcrystalline. The phenocrysts are approx. < 1mm and consist of plagioclase laths, pyroxene and opaques, in that order of abundance, with pyroxenes nearly as abundant as the feldspars. Original ASTER Spectral Library name was jhu.becknic.rock.igneous.intermediate.solid.andesi1.spectrum.txt
Composition:

Petrographic Description:  The modes for phenocrysts for this sample gave
26.75% plagioclase, 8.5% augite, 1.05% magnetite, 0.95% hypersthene, and
62.75% groundmass.  The groundmass for these samples consists of 
labradorite, augite, hypersthene, magnetite, ilmenite, trydimite as isolated grains and aggregates of small wedge-shaped crystals closely associated with small patches of intergrown granular quartz and chalcedony, anorthoclase, and  partly devitrified glass.

Microprobe Analysis:  The composition of the plagioclase phenocrysts was 
found to range from An59 to An62 (labradorite), while the composition in the groundmass ranged from An50 to An55.  The augite phenocryst composition was Wo 34%, En 43%, Fs 23%, that of the hypersthene phenocrysts was En 67%, Fs 33%.  Augite in the groundmass was W0 24%, En 45%, Fs 31%.

Chemical Analysis:
SiO2  57.20
CaO  8.85
TiO2  0.54
Na2O  2.50
Al2O3  16.35
K2O  0.68
Fe2O3  2.23
H2O  0.90
FeO  5.93
P2O5  0.36
MnO  0.14
MgO  4.65
TOTAL  100.3
