TITLE: Grossular NMNH155371 Garnet DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: NMNH155371

MINERAL_TYPE: Nesosilicate

MINERAL: Grossular (Grossularite) (Garnet group)

FORMULA: Ca3Al2(SiO4)3

FORMULA_HTML: Ca3Al2(SiO4)3

COLLECTION_LOCALITY: Pear Gillis Farm, Beach Glen, Buncombe Co, N.C

ORIGINAL_DONOR: Smithsonian

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Forms series with Andradite, with Hydrogrossular, with Uvarovite.

Sample was hand-picked for analysis. See other grossular garnet in library for comparison. Original sample had a fair amount of diopside contamination.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

Sample is grossular plus a small peak at 1.879A due to a trace of an unknown contaminant.

Salisbury, J. W., Walter, L. W., and Vergo, N., 1987, Mid-Infrared (2.1-25µm) Spectra of Minerals: First Edition, U.S. Geological Survey Open File Report 87-263.

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: EM(WDS) # XRF, EM(WDS), ICP(Trace), WChem

COMPOSITION: SiO2 38.84 wt% SiO2
COMPOSITION: TiO2 0.70 wt% TiO2
COMPOSITION: Al2O3 17.95 wt% Al2O3
COMPOSITION: FeO 7.08 wt% FeO
COMPOSITION: MnO 0.51 wt% Mn0
COMPOSITION: MgO 0.15 wt% MgO
COMPOSITION: CaO 35.81 wt% CaO
COMPOSITION: Na2O 0.05 wt% Na2O
COMPOSITION: K2O 0.03 wt% K2O
COMPOSITION: Total 101.11 wt%
COMPOSITION: O=Cl,F,S wt%
COMPOSITION: New Total wt%

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

Microprobe analysis of the hand-picked sample indicate the grains are relatively homogeneous, with approximately 1 wt% variation in FeO and CaO. Average of 11 analyses indicte this sample is a solid-solution grossulerite with andradite.

Salisbury, J. W., Walter, L. W., and Vergo, N., 1987, Mid-Infrared (2.1-25µm) Spectra of Minerals: First Edition, U.S. Geological Survey Open File Report 87-263.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

mode:
97 vol% garnet
3 vol% diopside

avg gr sz = 45 µm

Some biaxial, moderate relief grains present- probably diopside contaminant mentioned in sample description open file report. Sample composed of isotropic grains with refractive index > glycerin. Platey habit indicates parting. All observations consistent with this sample being nearly prue grossularite. G. Swayze

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1_2_3_4_

LIB_SPECTRA_HED: where Wave Range Av_Rs_Pwr Comment

LIB_SPECTRA: splib04a r 1835 0.2-3.0µm 200 g.s. = 45 µm

LIB_SPECTRA: splib05a r ____ 0.2-3.0µm 200 g.s.=

LIB_SPECTRA: splib06a r ____ 1.5-25µm 250 g.s.=