TITLE: Andesine HS142 Plagioclase DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS142

MINERAL_TYPE: Tectosilicate

MINERAL: Andesine (Plagioclase)(Feldspar group)

FORMULA: (Na,Ca)Al(Al,Si)Si2O8

FORMULA_HTML: (Na,Ca)Al(Al,Si)Si2O8

COLLECTION_LOCALITY: Montana

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Andesine is a plagioclase feldspar series mineral whose end members are albite (Na) and anorthite (Ca). Andesine falls into the 30-50% anorthite category in this series.

This sample is a mixture of different phases and was labeled andesine porphyry. The mineral mode confirms this. Average grain size is 40um. This sample could benefit from magnetic separation.

74-250µm sieve interval.

The spectrum indicates a weak absorption band near 2.2-2.3 µm, apparently due to trace alteration not detected by other methods. Roger N. Clark

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 6.5-9.5 keV
File: andes142.mdi, *.out; ands142b.mdi, *.out (smear mount on quartz plate)
References: Huebner's reference patterns
Found: Plagioclase, K-feldspar, quartz, trace of orthopyroxene

Comment: The feldspars were deciphered using patterns for low albite (WAR-0612) and microcline (Felix Chayes' 37A15). All peaks are very sharp indicating a high degree of crystallinity and compositional homogeneity. The two feldspar patterns are distinct.

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

END_XRD_ANALYSIS.

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

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

No compositional analyses available

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Optical examination gives the following mineral mode:

66 vol% andesine
25 vol% quartz
8 vol% altered andesine (Fe-stained)
1 vol% hornblend

av gr sz plag = 290µm
av gr sz qtz = 270µm
av gr sz populations = 285µm

This sample is a mixture of different phases and was labeled andesine porphyry. The mineral mode confirms this. This sample could benefit from magnetic separation. Plagioclase has low relief and synthetic twining. 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 356 0.2-3.0µm 200 g.s.= 285 µm

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

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