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: MedHi Al-muscovite +others CU91-252D DESCRIPT

DOCUMENTATION_FORMAT: MIXTURE

SAMPLE_ID: CU91-252D

MIXTURE_TYPE: Intimate

MIXTURE: MedHi Al-muscovite + quartz + clinochlore + goethite

FORMULA: KAl2(Si3Al)O10(OH,F)2 + SiO2 + (Mg,Fe2+)5Al(Si3Al)O10(OH)8 + alpha-FeO(OH)

FORMULA_HTML: KAl₂(Si₃Al)O₁₀(OH,F)₂ + SiO₂ + (Mg,Fe²⁺)₅Al(Si₃Al)O₁₀(OH)₈ + alpha-FeO(OH)

COLLECTION_LOCALITY: Western Alteration Center, Cuprite, Nevada, USA

ORIGINAL_DONOR: Gregg Swayze

COLLECTION_LATITUDE: N37 31.75' # degrees and decimal minutes (N or S)

COLLECTION_LONGITUDE: W117 13.77' # degrees and decimal minutes (W or E)

DATUM: NAD27 # coordinate datum

CURRENT_SAMPLE_LOCATION: U.S.G.S. Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: U.S.G.S. Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

This sample was collected 200 meters west of the southwestern end of the western alteration center at Cuprite, NV. The sample is from lower Cambrian Harkless Phyllite.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

Quartz (major), muscovite (mostly 2M1 with a trace of 1M polytypes), clinochlore (trace). Absence of XRD detection of goethite may be due to its presence as a thin coating or its fine grained crystal size. Jarosite may not be abundant enough to be detected by XRD.

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: XRF # XRF, EPMA, ICP(Trace), WChem

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

None

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

None

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

The spectrum has absorptions characteristic of a number of minerals. In the electronic region (0.35 - 1.35 microns) absorptions resembling those of goethite are spectrally dominant. The goethite absorptions are superimposed on those of clinochlore. The first OH overtone band of muscovite is located at 1.4101 microns while the Al-OH combination band is located at 2.1998 microns. The octahedral aluminum content is determined from this combination band wavelength location using an equation described in Figure 9 of Swayze and others (2014). A weak absorption at 2.257 microns may indicate the presence of jarosite, perhaps under the goethite coating.

See: Swayze, G.A., Clark, R.N., Goetz, F.H., Livo, K.E., Breit, G.N., Kruse, F.A., Sutley, S.J., Snee, L.W., Lowers, H.A., Post, J.L., Stoffregen, R.E. and Ashley, R.P., 2014, Mapping advanced argillic alteration at Cuprite, Nevada using imaging spectroscopy: Economic Geology, v. 109, no. 5, p. 1179-1221. DOI:10.2113/econgeo.109.5.1179

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1c2_3_4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns