Clark and others 2007 USGS Data Series 231
Spectral Library splib06a Sample Description

(For further information on spectroscopy, see: http://speclab.cr.usgs.gov)

TITLE: Grossular HS113 Garnet DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS113

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.

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:

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

Grossular + feldspar + others (Norma Vergo, USGS)

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EM(WDS), 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

LIB_SPECTRA_HED:	where	Wave Range	Av_Rs_Pwr	Comment
LIB_SPECTRA:	splib04a r 1824	0.2-3.0µm	200	g.s.= 300 µm
LIB_SPECTRA:	splib05a r 2930	0.2-3.0µm	200	g.s.=
LIB_SPECTRA:	splib06a r 8517			g.s.=
LIB_SPECTRA:	splib06a r 8529			g.s.=