TITLE: Bytownite HS106 Plagioclase DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS106

MINERAL_TYPE: Tectosilicate

MINERAL: Bytownite (Plagioclase)(Feldspar group)

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

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

COLLECTION_LOCALITY: Crystal Bay, Minnesota

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Bytownite is a plagioclase feldspar series mineral whose end members are albite (Na) and anorthite (Ca). Bytownite falls into the 70-90% anorthite category in this series.

Sieve interval 74-250µm.

This sample shows a nice plagioclase feldspar absorption feature near 1.2 µm, but the 2.0-µm band and bands longer than about 2.3 µm are due to water from a contaminant. Roger N. Clark

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 6.5-9.5 keV
File: bytwn106.mdi, *.out (smear mount on quartz plate)
References: Huebner's reference patterns, Borg and Smith (1969), HS-201.3B (anorthite)

Comment: A moderate intensity reflection at 2.783 anstroms is in the position of the anorthite (221) but is anomalously strong. Two very weak blips at 2.426 and 2.426 are consistent with Fe2O3 composition. Two quartz reflections [a weak (101) and strong!! (211)] are present in the coarse smear but are absent in the finely-ground material. Apparently the quartz reflections are due to non-random distribution of grains. The grains are soft. Talc

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

40 kV - 30 mA, 6.5-9.5 keV
File: bytwn106.mdi, *.out (smear mount on quartz plate)
Reference: Huebner's reference patterns, Borg and Smith (1969), HS-201.3B (anorthite)

Found: Calcic plagioclase consistent with bytownite
Comment: A moderate intensity reflection at 2.783 angstroms is in the position of the anorthite (221) but is anomalously strong. Two very weak blips at 2.426 and 2.426 may be background rather than reflections. Very narrow, strong bytownite reflections indicate a high degree of crystallinity and compositional homogeneity.

END_XRD_ANALYSIS.

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

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

No compositional analyses.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Optical examination gives the following mineral mode:

96 vol% bytownite
4 vol% sphene or garnet

av gr sz = 290µm

Clear rectangular grains with two cleavages, and twins. Biaxial (+) 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 776 0.2-3.0µm 200 g.s.= 290µm

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

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