TITLE: Almandine HS114 Garnet DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS114

MINERAL_TYPE: Nesosilicate

MINERAL: Almandine (Garnet group)

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

FORMULA_HTML: Fe+23Al2(SiO4)3

COLLECTION_LOCALITY: Warren County, New York

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Forms series with Pyrope and with Spessartine.

"This is a common garnet of schists and gneisses and also occurs in intermediate to acidic igneous rocks. It is the most widespread variety of garnet found as a detrital mineral in sedimentary rocks. Again, this spectrum is dominated by the intense absorption at 1.28 µ and 1.7 µ due to the ferrous iron in eight-fold coordination. Also, there is a rapid fall off to the blue caused by both ferrous and ferric ion absorptions. The well defined band at 0.7 µ confirms the presence of Fe+3 substituted for Al+3, and the suggestion of a band near 0.85µ in the smallest particle size is consistent with this - even though the combination of the visible and near-infrared intense absorptions provide a well-resolved maximum near 0.85 µm, especially in the larger particle size samples. The visible spectrum shows features at 0.37, 0.43, 0.51, and 0.57 µ, which is quite similar to the spectrum of spessartine, with the exception of the very sharp 0.41 µ Mn+2 band, which is absent."

Hunt, G.R., J.W. Salisbury, and C.J. Lenhoff, 1973, Visible and near-infrared spectra of minerals and rocks: VI. Additional silicates. Modern Geology, v. 4, p. 85-106.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 7.3 -9.5 keV
File: alma114.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; very weak unindexed reflection at 2.29 angstroms

Comment: Very sharp reflections indicate excellent crystallinity and suggest compositional homogeneity. Garnet ao=11.51+/-3 angstroms, consistent with almandine composition (at 11.526 angstroms). Unusual rise in background centered about 42 degrees 2 theta.

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

END_XRD_ANALYSIS.

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


COMPOSITION: SiO2 40.40 wt% SiO2
COMPOSITION: TiO2 0.07 wt% TiO2
COMPOSITION: Al2O3 22.97 wt% Al2O3
COMPOSITION: Cr2O3 0.01 wt% Cr2O3
COMPOSITION: V2O3 0.01 wt% V2O3
COMPOSITION: FeO 22.45 wt% FeO
COMPOSITION: NiO 0.02 wt% NiO
COMPOSITION: MnO 0.53 wt% MnO
COMPOSITION: MgO 11.05 wt% MgO
COMPOSITION: CaO 4.27 wt% CaO
COMPOSITION: Total 101.79 wt%
COMPOSITION: O=Cl,F,S wt% #correction for Cl, F, S
COMPOSITION: New Total 101.79 wt%

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

None.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

av gr sz = 260µm

Conchoidally fractured grains, isotropic under cross-polarized light. About 3% thin fibrous inclusions. 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 140 0.2-3.0µm 200 g.s.= 260 µm

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

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