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(For further information on spectrsocopy, see:
http://speclab.cr.usgs.gov)
TITLE: Gibbsite HS423 DESCRIPT
DOCUMENTATION_FORMAT: MINERAL
SAMPLE_ID: HS423
MINERAL_TYPE: Hydroxide
MINERAL: Gibbsite
FORMULA: Al(OH)3
FORMULA_HTML: Al(OH)3
COLLECTION_LOCALITY: Brazil
ORIGINAL_DONOR: Hunt and Salisbury Collection
CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory
SAMPLE_DESCRIPTION:
Trimorphous with Bayerite and Nordstrandite.
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 comment:"This particular sample is a cryptocrystalline stalactitic aggregate, composed of concentric layers of gibbsite of variable purity. Some layers are slightly contaminated with iron, which produces the gentle fall-off in reflectivity of the powdered samples toward the blue region of the visible. In the near-infrared, all the spectral features are due to the vibrations of the hydroxyl ion. In the mid-infrared, well defined fundamental Al-O-H bending modes occur at 10.34 and 9.8µm, and a series of fundamental stretching modes occur at 2.975, 2.917, 2.842, and 2.765µm. The second overtone and combinations of the stretching modes produce the weak but relatively sharp features which appear near 1.0µm in our spectra, the first overtone and combinations of the stretching mode produce the numerous relatively sharp features centered at 1.45µm, and the combinations of the stretching and bending modes produce the features near 2.3µm. Some free water is indicated by the bands near 1.9µm."
END_SAMPLE_DESCRIPTION.
XRD_ANALYSIS:
Pure gibbsite
Konnert, Judith and Marta Flohr, 1992, unpublished data, USGS Reston, VA.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:
mode:
94 vol% gibbsite
6 vol% Fe-stained gibbsite grains
average grain size= 60 µm
Concentric dark lines of inclusions across crystal bundles indicates growth as stalatitic forms. Inclined extinction, small 2V (<20 degrees), biaxial (+), all consistent with gibbsite. G. Swayze.
END_MICROSCOPIC_EXAMINATION.
SPECTROSCOPIC_DISCUSSION:
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: | splib04a r 1739 | 0.2-3.0µm | 200 | g.s.= 60 µm |
| LIB_SPECTRA: | splib05a r 2793 | 0.2-3.0µm | 200 | g.s.= |
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