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 WS220 DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: WS220

MINERAL_TYPE: Hydroxide

MINERAL: Goethite

FORMULA: alpha-FeO(OH)

FORMULA_HTML: alpha-FeO(OH)

COLLECTION_LOCALITY: Kent, Connecticut

ORIGINAL_DONOR: Wards Natural Science Inc.

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Polymorphous with Akaganeite, Feroxyhyte, and Lepidocrocite.

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 7.3-9.5 keV
File: gotht220_mdi, *.out (smear mount on quartz plate)
Found: quartz, minor goethite

Comment: Superbly sharp quartz reflections of moderate overall intensity indicates excellent crystallinity. Very weak, broad goethite reflections indicate poor crystallinity and possible low abundance (compare with "pure" goethite, GDS-134). Amorphous material 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:

mode:
60 vol% quartz
20 vol% large goethite grains
20 vol% small goethite grains

Bimodal goethite grain size distribution:
mode 1: average grain size= 50 µm @ 50 vol%
mode 2: average grain size= 10 µm @ 50 vol%
average grain size= 36 µm

quartz average grain size= 75 µm

Significant quartz contamination, quartz is 50% coated by goethite. Large goethite grains are 50% coated with smaller goethite grains. High relief, non-fibrous, platey (lepidochrosite?). Slight red pleochroism. G. Swayze.

The high quartz content reduces the strength of the saturated UV-Vis absorption bands, otherwise spectrally pure. R. Clark

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1c2_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 1813	0.2-3.0µm	200	g.s.= 36 µm
LIB_SPECTRA:	splib05a r 2891	0.2-3.0µm	200	g.s.=

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U.S. Department of the Interior | U.S. Geological Survey URL: https://pubsdata.usgs.gov/pubs/of/2003/ofr-03-395/DESCRIPT/M/goethite_ws220.html Questions or Assistance: USGS Web Contact Page Last Modified: Sat Jan 12 23:31 EDT 2013