Oligoclase

Spectrum Details

Modality

FTIR

Category

mineral

Material Type

Tectosilicate

Sample ID

HS110.3B

Collection Locality

Mitchell Co., New York

Spectral Purity

1c2b3b4_ # HS110.3B # 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:

Sample Description

Most analyses contain small amounts of Na, but a complete solid solution series is possible from orthoclase toward intermediate albite. Crystallizes at intermediate temperatures and has a partially ordered Al-Si distribution. Sieve interval 74-250µm. "Oligoclase's are composed of from 70 to 90% albite and 30 to 10% anorthite. This pure white sample contains very little muscovite impurity. Its spectrum is quite flat with broad 1.4µm, 1.9µm, and weak 2.2µm features. The 1.9 band is indicative of the presence of a small amount of included H20, while the 2.2µm feature is due to the OH stretch-AlOH bending combination." Hunt, G.R., J.W. Salisbury, and C.J. Lenhoff, 1973, Visible and near-infrared spectra of minerals and rocks: VI. Additional silicates. Modern Geology, v. 4, p. 85-106. IMAGE_OF_SAMPLE:

XRD Analysis

40 kV - 30 mA, 6.5-9.5 keV File: oligo110.mdi (quartz smear mount) References: Huebner's reference patterns; Borg and Smith (1969); Kroll (1983) Found: Plagioclase feldspar (oligoclase or intermediate albite), minor quartz Comments: Sharp peaks show good resolution of alpha1-alpha2 components, suggesting good crystallinity and homogeneity of compositional and structural state. Peaks assumed to be the quartz (100) and (101) were used as an internal standard. All other peaks were indexed following Borg and Smith (1969) for oligoclase. Refinement of 43 reflections gave a=8.169(2), b=12.846(2), c=7.140(2) Angstroms, alpha=93.99(3), beta=116.47(2), gamma=88.87(2). Five unit cell parameters and the value of delta2theta(1-31)-(131) corresponded to a bulk composition less than 30% anorthite component (The a dimension indicates An=60%). The cell dimensions do not constrain the structural state. If HS110 is an alkali feldspar, the criteria of Wright (1968) indicate composition Ab96Or4 and intermediate structural state. Line- and profile-based search-match routines return ordered oligoclase (41-1480) and disordered albite (10-0393) as the most likely hits. Visually, the ordered oligoclase gives a distinctly superior fit.

X Units

cm⁻¹

Y Units

Absorbance

Data Points

1,801