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(For further information on spectroscopy, 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
IMAGE_OF_SAMPLE:
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 described 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: 1c2c3c4_ # 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.= |
| LIB_SPECTRA: | splib06a r 2146 | g.s.= | ||
| LIB_SPECTRA: | splib06a r 2160 | g.s.= |