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: Alunite GDS82 Na82 DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: GDS82

MINERAL_TYPE: Sulfate

MINERAL: Alunite (Alunite Group)

FORMULA: (Na,K)Al3(SO4)2(OH)6

FORMULA_HTML: (Na,K)Al₃(SO₄)₂(OH)₆

COLLECTION_LOCALITY: Sadler, Texas, USA

ORIGINAL_DONOR: Roger Soffregen

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Low temperature diagenetic variety of alunite. May be from a lake deposit. Composition is 82 mole% Na by atomic absorption: See: Stroffregen, R., and Alpers, C., 1992, Observations on the unit-cell dimensions, H2O contents and del D values of natural and synthetic alunite: American Mineralogist, v.77, p. 1092-1098.

IMAGE_OF_SAMPLE:

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

GDS82 Na-(82) alunite 40 kV - 30 mA, 6.5-9.5 keV (n8Oalnt.out) References: JCPDS #41-1467; Huebner's reference patterns Found: alunite, quartz, very very weak reflections at 2.38 and 1.720 A. Comment: the alunite is probably a single phase; its lattice spacing's match those of natroalunite. The alunite has sharp peaks, indicating good crystallinity and compositional homogeneity

see: Stroffregen, R., and Alpers, C., 1992, Observations on the unit-cell dimensions, H2O contents and del D values of natural and synthetic alunite: American Mineralogist, v.77, p. 1092-1098.

END_XRD_ANALYSIS.

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

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

Sample is a standard used by: Stroffregen, R., and Alpers, C., 1992, Observations on the unit-cell dimensions, H2O contents and del D values of natural and synthetic alunite: American Mineralogist, v.77, p. 1092-1098.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

mode 1: 70 microns @55 vol% mode 2: 3 microns @45 vol% avg. grain size= 50 microns Larger grains have extinction characteristic of very fine grained aggregates. Cannot determine the optical properties because of small grain size. Trace opaques. Purity confirmed by XRD by: Roger Stroffregen. & G., Swayze.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

Sample has weak vibrational features between 1.4 - 1.5, 1.76, 2.17, and 2.33 microns.

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1b2b3c4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns