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USGS Spectral Library Version 7 Sample Description

Kokaly, R.F., Clark, R.N., Swayze, G.A., Livo, K.E., Hoefen, T.M., Pearson, N.C., Wise, R.A., Benzel, W.M., Lowers, H.A., Driscoll, R.L., and Klein, A.J., 2017, USGS Spectral Library Version 7: U.S. Geological Survey Data Series 1035, 61 p., https://doi.org/10.3133/ds1035
For more information on the library, see: local link web link

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.

IMAGE_OF_SAMPLE:
Photo of sample

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, EPMA, 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, platy (lepidocrocite?). 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: 1c2c3d4_ # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns