MINERAL: Grossular (Grossularite) (Garnet group)
COLLECTION_LOCALITY: Laguna de Jaco, Chihuahua, Mexico
ORIGINAL_DONOR: Wards Natural Science Inc.
CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
Forms series with Andradite, with Hydrogrossular, with Uvarovite.
40 kV - 30 mA, 6.5-9.5 keV
File: gros483.out, *.mdi (smear mount on quartz plate)
References: Borg and Smith (1969), JCPDS #39-368, DHZ, v. 1a (1982), Huebner's reference patterns
Comment: Moderately sharp reflections; some peaks appear to be closely-spaced doublets. This garnet is probably well crystallized with some compositional heterogeneity. The ao=11.85 Angstroms, consistent with grossular. Only one cell dimension could be resolved, but the shape of some peaks suggests limited solid-solution toward andradite (or uvarovite).
J.S. Huebner, J. Pickrell, T. Schaefer, written communication 1994
COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EPMA, ICP(Trace), WChem
98 vol% garnet
2 vol% diopside?
Bimodal grains size distribution:
mode 1: 180 µm @ 70 vol%
mode 2: 10 µm @ 30 vol%
average grain size= 150 µm
About 2 vol% grains have high interference colors and cleavage (diopside?) but these are limited to the smaller grains size population. Other grains are isotropic, with conchoidal fractures, and have refractive index > glycerin. All this is consistent with a slightly contaminated garnet sample. G. Swayze.
SPECTRAL_PURITY: 1b2c3c4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns