Sample Description USGS Spectral Library Version 7

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
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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:

IMAGE_OF_SAMPLE: photo of bulk sample

END_SAMPLE_DESCRIPTION.

XRD_ANALYSIS:

40 kV - 30 mA, 6.5-9.5 keV

References: Tada and Iijima (1983), Isaacs and others (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J.S. Huebner, J Pickrell, T. Schaefer, unpublished data, written communication, USGS, Reston, VA (1994)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 and others (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, EPMA, ICP(Trace), WChem

COMPOSITION_TRACE: None

COMPOSITION_DISCUSSION:

None

END_COMPOSITION_DISCUSSION.

MICROSCOPIC_EXAMINATION:

Lots of Fe-staining in photograph. G. Swayze.

END_MICROSCOPIC_EXAMINATION.

SPECTROSCOPIC_DISCUSSION:

Fe-staining seen in photograph of sample may contribute to downturn into UV. G. Swayze.

END_SPECTROSCOPIC_DISCUSSION.

SPECTRAL_PURITY: 1a2a3a4_ # TM8896 # 1= 0.2-3, 2= 1.5-6, 3= 6-25, 4= 20-150 microns