Opal

Spectrum Details

Modality

FTIR

Category

mineral

Material Type

Tectosilicate

Sample ID

TM8896

Collection Locality

Beaver Co., UT.

Spectral Purity

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

Composition / XRD

None # XRF, EPMA, ICP(Trace), WChem COMPOSITION_TRACE: None

Sample Description

IMAGE_OF_SAMPLE: photo of bulk sample

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 J.S. Huebner, J Pickrell, T. Schaefer, unpublished data, written communication, USGS, Reston, VA (1994) 40 kV - 30 mA, 6.5-9.5 keV File: opal8896.mdi (smear on quartz plate) References: Isaacs and others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.

X Units

cm⁻¹

Y Units

Absorbance

Data Points

1,801