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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: Almandine WS475 Garnet DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: WS475

MINERAL_TYPE: Nesosilicate

MINERAL: Almandine (Garnet group)

FORMULA: (Fe+2)3Al2(SiO4)3

FORMULA_HTML: Fe+23Al2(SiO4)3

COLLECTION_LOCALITY: Jackson Co., North Carolina

ORIGINAL_DONOR: Wards Science

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Forms series with Pyrope and with Spessartine.

Optical examination gives the following mode:

95 vol% almandine
4 vol% biotite
1 vol% magnetite

Rose pink color in hand sample, original sample was a almandine-biotite schist. Sample was hand-picked and sieved so that current sample consists of < 250-µm grain fraction. Sample could benefit from more handpicking under a microscope. Biotite forms almandine coated flakes.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 7.3-9.5 keV
File: alma475.out, *_mdi (smear mount on quartz plate)
References: Borg and Smith (1969), JCPDS #9-427, DHZ, v. 1a (1982), Huebner's reference patterns
Found: Garnet, minor mica, trace kaolin mineral, unidentified reflection at 4.59 angstroms

Comment: All reflections sharp, indicating good crystallinity. Resolved three distinct garnet compositions; the major garnet has ao=11.51 angstroms, consistent with almandine-rich garnet; the minor garnets have larger ao (to 11.57 angstroms) indicating solid solution, perhaps with spessartine or grossular. Mica identification was based on two basal reflections, each a doublet (two mica compositions?). The kaoline mineral identification was also based on two basal reflections; that at 7 angstroms is also a doublet! This is an unusual assemblage; was the sample contaminated during collection or preparation?

J.S. Huebner, J. Pickrell, and T. Schaefer, 1994, written communication.

END_XRD_ANALYSIS.

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


COMPOSITION
KEYWORD
Oxide
ASCII
Amount Weight
Percent, %
Oxide
html
COMPOSITION: SiO2 37.98 wt% SiO2
COMPOSITION: TiO2 0.00 wt% TiO2
COMPOSITION: Al2O3 22.14 wt% Al2O3
COMPOSITION: Cr2O3 0.01 wt% Cr2O3
COMPOSITION: V2O3 0.01 wt% V2O3
COMPOSITION: FeO 29.83 wt% FeO
COMPOSITION: NiO 0.01 wt% NiO
COMPOSITION: MnO 0.47 wt% MnO
COMPOSITION: MgO 7.35 wt% MgO
COMPOSITION: CaO 1.71 wt% CaO
COMPOSITION: Total 99.52 wt%
COMPOSITION: O=Cl,F,S wt% #correction for Cl, F, S
COMPOSITION: New Total 99.52 wt%

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

Microprobe analyses are average of five spot locations done on different grains. All Fe is expressed as FeO, and the Fe2O3 content
was not determined.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Optical examination gives the following mineral mode:

95 vol% pyrope
4 vol% biotite
1 vol% magnetite or other opaque

This sample has a bimodal grain size distribution:

1st population: avg grain size = 200 µm
2nd population: avg grain size = 25 µm

avg. grain size = 199 µm

Smaller grains partially coat larger grains. G. Swayze

Fine pyrope grains adhere to biotite contaminant surfaces. Some pyrope grains (~10%) have dark honey color perhaps due to mafic inclusions. Most grain surfaces have conchoidal fractures since garnet has no cleavage; parting surfaces not apparent in this sample.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1b2_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 151 0.2-3.0µm 200 g.s.= 199 µm
LIB_SPECTRA: splib05a r 208 0.2-3.0µm 200 g.s.=


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