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Clark et. al. 2003 USGS Open File Report 03-395
Spectral Library splib05a Sample Description

(For further information on spectrsocopy, see: http://speclab.cr.usgs.gov)

TITLE: Holmquistite HS291 Amphibole DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS291

MINERAL_TYPE: Inosilicate

MINERAL: Holmquistite (Amphibole group)

FORMULA: Li2(Mg,Fe+2)3Al2Si8O22(OH)2

FORMULA_HTML: Li2(Mg,Fe+2)3Al2Si8O22(OH)2

COLLECTION_LOCALITY: Quebec

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Forms series with Ferroholmquistite and Magnesioholmquistite_
Dimorphous with Clinoholmquistite.

"I-20 Holmquistite 291B--Quebec, Li2(Mg,Fe2+)3(Al, Fe3+)2(Si8O22)(OH,F)2): Holmquistite is a rare amphibole, the main occurrences of which are located at or close to the contact between lithium-rich pegmatites and country rocks. There are broad general absorption bands in the spectrum of this sample centered near 0.7 and 1.0µ due to Fe3+ and Fe2+. The weak OH feature near 1.4µ is accompanied by a considerably stronger OH band at 2.35µ. As in the cases of the tremolite and riebecite above, the
additional strength and slight positive shift of the 2.35µ band is due to a small contribution from a carbonate contaminant. The low reflectivity and poorly defined bands are a result of the presence of opaque magnetite and pyrite as impurities."

Sieve interval 74 - 250µm.

Hunt, G.R., J.W. Salisbury, and C.J. Lenhoff, 1973, Visible and near-infrared spectra of minerals and rocks: VI. Additional silicates. Modern Geology, v. 4, p. 85-106.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV- 30 mA, 7.0-9.5 keV
File: holmq291.out, -.mdi
References: Huebner's reference patterns
Found: K-mica, orthoamphibole, minor chlorite and K-feldspar, trace quartz

Comment: Peaks are sharp; the constituent minerals appear well-crystallized and compositionally homogenous. The amphibole has lattice spacing's consistent with the characteristic cell dimensions of holmquistite. Not all peaks were indexed; a fifth phase may be present.

END_XRD_ANALYSIS.

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

COMPOSITION_TRACE:

None

COMPOSITION_DISCUSSION:

None

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Sample is very contaminated with:

Mode:

40 vol% Anthophyllite ? biaxial (-), parallel extinction
40 vol% Plagioclase (altered to sericite?)
17 vol% quartz (uniaxial +)
3 vol% Holmquistite (light blue color in plane light)

If Holmquistite is the light blue amphibole with parallel extinction and amphibole cleavage (biaxial -), then this mineral only forms 3 vol% of the contents of this bottle. I suggest sample be X-rayed to see if green amphibole is the Holmquistite or anthophyllite. If the green amphibole turns out to be Holmquistite, then it may be separated using heavy liquids or Franz separator. If blue mineral is Holmquistite then these separation procedures will probably not give enough Holmquistite to make the effort worthwhile.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1d2_3_4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns

LIB_SPECTRA_HED: where Wave Range Av_Rs_Pwr Comment
LIB_SPECTRA: splib04a r 2164 0.2-3.0µm 200 g.s.=
LIB_SPECTRA: splib05a r 3320 0.2-3.0µm 200 g.s.=


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