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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: Opal TM8896 (Hyalite) DESCRIPT

DOCUMENTATION_FORMAT: MINERAL

SAMPLE_ID: TM8896

MINERAL_TYPE: Tectosilicate

MINERAL: Opal

FORMULA: SiO2*nH2O

FORMULA_HTML: SiO2•nH2O

COLLECTION_LOCALITY: Beaver Co., UT.

ORIGINAL_DONOR: Jim Piper

CURRENT_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

ULTIMATE_SAMPLE_LOCATION: USGS Denver Spectroscopy Laboratory

SAMPLE_DESCRIPTION:

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 6.5-9.5 keV

References: Tada and Iijima (1983), Isaacs et al. (1983)
Found: mixture of opal-A and opal-CT
Comment: A good opal. Broad maximum centered at 22 degrees, very poor degree of crystallinity. Opal-CT has a very weak reflection at position of quartz (101). I have no basis for estimating the relative proportions of these the two forms of opal - rather, they form a progression as longer-range order develops.

J.S. Huebner, J Pickrell, T. Schaefer, unpublished data, written communication, USGS, Reston, VA (1994)

40 kV - 30 mA, 6.5-9.5 keV
File: opal8896.mdi (smear on quartz plate)
References: Isaacs et al. (1983); Tada and Ijima (1983)
Found: opaline phase

Comment: There is only one very weak and broad peak, in the position of the usually intense and sharp quartz (101) reflection at 3.35 angstroms. The observed broad rise centered around 4.00 angstroms is consistent with opaline silica. Possibly significant maxima on the broad rise are in positions of cristobalite and tridymite, but there are no corresponding peaks at smaller interplanar spacing's. The material is most likely transitional between opal-A and opal-CT states.

END_XRD_ANALYSIS.

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

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

None

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

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 3755 0.2-3.0µm 200 g.s.=
LIB_SPECTRA: splib05a r 5256 0.2-3.0µm 200 g.s.=


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