U.S. Geological Survey home page


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 HS36 DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: HS36

MINERAL_TYPE: Hydroxide

MINERAL: Goethite

FORMULA: alpha-FeO(OH)

FORMULA_HTML: alpha-FeO(OH)

COLLECTION_LOCALITY: Biwabik, Minn

ORIGINAL_DONOR: Hunt and Salisbury Collection

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

Polymorphous with Akaganeite, Feroxyhyte, and Lepidocrocite.

Original spectrum published in: Hunt, G.R., J.W. Salisbury, and C.J. Lenhoff, 1971, Visible and near-infrared spectra of minerals and rocks: III. Oxides and hydroxides. Modern Geology, v. 2, p. 195-205.

With the note:"Like cuprite, goethite displays trans-opaque behavior, but does so at a slightly shorter wavelength (near 0.55µm). The ferric ion itself produces the feature near 0.9, and the fall-off short of 0.55µm is explained as being due to the presence of a conduction band with a quite well-resolved absorption edge, which is typical of the trans-opaque iron oxides. It should be noted in particular that goethite displays no hydroxyl bands in the near-infrared, despite its traditional formula, FeO-OH. Like diaspore (see above), the pure mineral should contain no free hydroxyl groups (Ewing, 1935)."

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 7.3-9.5 keV
File: gotht36_mdi, *.out (smear mount on quartz plate)
References: Huebner's reference patterns
Found: goethite, minor quartz, unidentified reflection at

Comment: Goethite reflections are moderately sharp, indicating moderate degree of crystallinity. Quartz (primarily the (100) reflection) is very sharp but weak.

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:
90 vol% fibrous goethite
10 vol% quartz or other clear mineral
trace paper fibre
trace metal shavings from grinder

Bimodal grain size distribution:
mode 1: average grain size = 300 µm @ 98 vol%
mode 2: average grain size = 10 µm @ 2 vol%

average grain size = 297 µm

*above grain size for goethite only; average grain size quartz = 150 µm

Fibrous brown grains (prismatic?), length slow, biaxial, high relief. Translucent red in plain polarized light. Grains are slightly pleochroic. These properties are consistent with goethite. Sample should be cleaned of iron shavings with a magnet. G. Swayze.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1b2_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 1792 0.2-3.0µm 200 g.s.= 300 µm
LIB_SPECTRA: splib05a r 2840 0.2-3.0µm 200 g.s.=


USA.gov logo  Take Pride in America button