Sample Description USGS Spectral Library Version 7

USGS Spectral Library Version 7 Sample Description

Kokaly, R.F., Clark, R.N., Swayze, G.A., Livo, K.E., Hoefen, T.M., Pearson, N.C., Wise, R.A., Benzel, W.M., Lowers, H.A., Driscoll, R.L., and Klein, A.J., 2017, USGS Spectral Library Version 7: U.S. Geological Survey Data Series 1035, 61 p., https://doi.org/10.3133/ds1035
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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: EPMA # XRF, EPMA, 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 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