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Clark et. al. 2003 USGS Open File Report 03-395
Spectral Library splib05a Sample Description

(For further information on spectrsocopy, see: http://speclab.cr.usgs.gov)

TITLE: Andradite GDS12 Garnet DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: GDS12

MINERAL_TYPE: Nesosilicate

MINERAL: Andradite (Garnet Group)

FORMULA: Ca3(Fe+3)2(SiO4)3

FORMULA_HTML: Ca3Fe+32(SiO4)3

COLLECTION_LOCALITY: Esmerald Co., Nevada

ORIGINAL_DONOR: Fred Kruse, University of Colorado

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Forms series with Grossular and with Schorlomite.

Sample is ground and sieved to less than 250 µm. Compare with other Andradite samples in library because spectral differences do exist between samples.

Spectral features near 2.3 µm indicate trace spectral contamination. From the analyses below and the band position and shape, this appears to be calcite. Roger N. Clark

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 7.3-9.5 keV
File: angds12.out, *.mdi
References: Huebner's reference patterns
Found: Garnet, probable clinopyroxene and alkali feldspar (two?)

Comment: Difficult pattern to decipher. Four garnet compositions are resolved; the dominant garnet has ao=11.87 angstroms, consistent with grossular-rich garnet. Other garnet compositions have larger cell dimensions (to ao=11.98 angstroms), indicating andradite or uvarovite component. Based on brown color, the minor garnet compositions are andradite-rich. Many weak to very weak reflections are best deconvoluted as a clinopyroxene (augite, not hedenbergite) and alkali feldspar (microcline + low albite). Optics are consistent; isotropic garnet, a low-birefringence phase with about 1.53 refractive index, and a moderate birefringence phase with about 1.69 refractive index.

END_XRD_ANALYSIS.

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


COMPOSITION
KEYWORD
Oxide
ASCII
Amount Weight
Percent, %
Oxide
html
COMPOSITION: SiO2 36.78 wt% SiO2
COMPOSITION: TiO2 0.14 wt% TiO2
COMPOSITION:Al2O3 6.62 wt% Al2O3
COMPOSITION: FeO 21.50 wt% FeO
COMPOSITION: MnO 0.98 wt% MnO
COMPOSITION: MgO 0.05 wt% MgO
COMPOSITION: CaO 33.89 wt% CaO
COMPOSITION: Total 99.96 wt%
COMPOSITION: O=Cl,F,S wt% #correction for Cl, F, S
COMPOSITION: New Total wt%

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

Al may replace Fe+3; Fe+2, Mn+2 and Mg may replace Ca.

Hurlbut, C.S., and C. Klein, 1977, Manual of Mineralogy. John Wiley, New York, 532P.

Compositional data compiled by G. Swayze, Branch of Geophysics, USGS Denver.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Conchoidally fractured grains, trace of opaques, under optical scope significant calcite contamination (10-20 vol%) and sample fizzes in dilute HCl acid. Grain size range 5-250 µm. G. Swayze

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1c2_3_4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns

LIB_SPECTRA_HED: where Wave Range Av_Rs_Pwr Comment
LIB_SPECTRA: splib04a r 367 0.2-3.0µm 200 g.s.=
LIB_SPECTRA: splib05a r 974 0.2-3.0µm 200 g.s.=


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