TITLE: Alunite GDS82 (Natroalunite) DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: GDS82

MINERAL_TYPE: Sulfate

MINERAL: Alunite (Na82) (Natroalunite) (Alunite group)

FORMULA: (Na,K)Al3(SO4)2(OH)6 Na82

FORMULA_HTML: (Na,K)Al3(SO4)2(OH)6 (Na82)

COLLECTION_LOCALITY: Sadler, TX

ORIGINAL_DONOR: Roger Stoffregen, SMU

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

This is a low temperature, diagentic variety of alunite.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 6.5-9.5 keV (n80alnt.out)
References: JCPDS #41-1467; Huebner's reference patterns
Found: alunite, quartz, very very weak reflections at 2.38 and 1.720 Angstroms.

Comment: the alunite is probably a single phase; its lattice spacings match those of natroalunite. The alunite has sharp peaks, indicating good crystallinite and compositional homogeneity"

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

END_XRD_ANALYSIS.

COMPOSITIONAL_ANALYSIS_TYPE: None # XRF, EM(WDS), ICP(Trace), WChem

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

Sample is a standard used by:

Stoffregen, 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:

Bimodal grain size distribution:
mode 1: 70 µm @ 55 vol%
mode 2: 3 µm @ 45 vol%

avg gr sz = 50 µm

Larger grains have extinction characteritic of very fine grained aggregates. I cannot determine the optical properties because of small grain size. Trace opaques. Purity confirmed by XRD by Roger Stoffregen. 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 226 0.2-3.0µm 200 g.s.= 50 µm

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

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