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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
For more information on the library, see: local link web link

TITLE: Grossular HS113.3B-HCL Garnt DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS113.3B-HCL

MINERAL_TYPE: Nesosilicate

MINERAL: Grossular (Grossularite) (Garnet group)

FORMULA: Ca3Al2(SiO4)3

FORMULA_HTML: Ca3Al2(SiO4)3

COLLECTION_LOCALITY: Transvaal, S. Africa

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 Andradite, with Hydrogrossular, with Uvarovite.

In this sample some ferrous ion has substituted for calcium, producing the 1.0 µm absorption and some ferric ion has substituted for aluminum, producing the band near 0.8 µm. Such substitution is common for this mineral. The presence of Fe
accounts for the absorption features near 0.6 and 0.43 µm and the series of bands between 1.4 and 1.51 µm are due to OH substitution for SiO4. Carbonate impurities cause absorption features near 2.25, 2.35, and 2.5 µm.

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.

Grain size fractions are indicated by the extension after the sample number:
.3B = 74-250 µm

See additional spectra of grossular garnets in library for comparison. This sample has been washed in HCl acid to remove carbonate contaminants.

IMAGE_OF_SAMPLE:
Photo of sample

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

Grossular + feldspar + others (Norma Vergo, USGS)

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EPMA, ICP(Trace), WChem

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

average grain size = 300 µm

Sample contains a trace of magnetite which can be cleaned with a magnet or Franz separator. Large garnet grains 15% coated by 8 µm garnet grains. Some of the thinner grains are isotropic, but the thicker grains have mottled extinction suggesting intense internal fracturing. Grains have high relief, high refractive index, rough fracture and no cleavage. Apart from the mottled extinction this sample resembles garnet. Sample tested with HCl acid and gave no fizz. G. Swayze.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1d2c3c4c # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns