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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: Goethite_Thin_Film WS222 DESCRIPT

DOCUMENTATION_FORMAT: MIXTURE

SAMPLE_ID: WS222

MIXTURE_TYPE: Coating # Areal, Intimate, Coating, or Molecular

MIXTURE: Goethite Coating on a thin section

FORMULA: alpha-FeO(OH)

FORMULA_HTML: alpha-FeO(OH)

COLLECTION_LOCALITY: Superior Mine, Marquette, Michigan

ORIGINAL_DONOR: Wards Natural Science Inc. prepared by Gregg Swayze

COLLECTION_LATITUDE: Not Available # degrees and decimal minutes (N or S)

COLLECTION_LONGITUDE: Not Available # degrees and decimal minutes (W or E)

DATUM: Not Available # coordinate datum

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Goethite WS222 sample was hand ground from botryoidal sample. Impurities were removed prior to grinding. This fine grained powder was mixed with water and an eye-dropper was used to deposit a thin coating on a microscope glass thin section. The sample was dried over night and them measured spectrally. Our goal was to unsaturate the goethite bands and mimic the spectral absorptions found in natural goethite coatings.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

Goethite
Perhaps some quartz

Konnert, Judith and Marta Flohr, 1992, unpublished data, U.S.G.S. Reston, VA.

END_XRD_ANALYSIS.

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

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

None.

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

For goethite powder:
Bimodal grain size distribution:
mode 1: avg. grain size = 227 µm @ 30 vol%
mode 2: avg. grain size = 5 µm @ 70 vol%

avg. grain size = 125 µm

No visible impurities; large fibrous grains are 90% coated with finer grains. High relief, moderate red pleochroism, prismatic cleavage. All this is consistent with pure goethite. G. Swayze.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

Spectrum has Fe-related absorptions characteristic of geothite. Bands are located at 0.5010, 0.6655, and 0.9412 microns. Of note is the narrow width of the 0.9412 micron band: it is only 250 nm wide -- much narrower than in spectra of powdered goethite samples. Apparently the band narrows most on the long wavelength side of this band in coatings.

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1a2_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: splib05a r 9113 0.2-3.0µm 200 g.s.=


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