The investigation of the optical properties of polytypic minerals

Simple item page
dc.contributor.authorCooper, Brian J.en
dc.contributor.committeechairRibbe, Paul H.en
dc.contributor.committeememberAlmeida, Silverio P.en
dc.contributor.committeememberBloss, F. Donalden
dc.contributor.committeememberCraig, James R.en
dc.contributor.committeememberIndebetouw, Guy J.en
dc.contributor.departmentGeological Sciencesen
dc.date.accessioned2015-06-24T13:35:33Zen
dc.date.available2015-06-24T13:35:33Zen
dc.date.issued1988en
dc.description.abstractA new approach to the investigation of the optical properties of polytypic minerals that combines spindle stage techniques, X-ray diffraction methods, electron microprobe analysis, and dielectric tensor calculations has been developed and applied to zinc sulfides and chloritoids. For the first time, X—ray diffraction studies of natural anisotropic zinc sulfides have documented the simultaneous occurrence of twinning and stacking disorder along more than one of the four symmetry equivalent <111> directions of sphalerite. Precession photographs of optically anisotropic zinc sulfides are characterized by twin—equivalent diffraction maxima and diffuse diffraction streaking along lattice rows with (h-k) ≠ 3n (equivalent hexagonal indices) in one or two <111> directions. A system of linear equations has been used to calculate the approximate volume fractions of each twin domain and the sphalerite host domain. Dielectric tensor calculations have been performed to illustrate that mixtures of cubic and hexagonal zinc sulfide may be optically biaxial if the intergrowth occurs along more than one of the symmetry equivalent <111> directions of sphalerite (cubic). The dependence of the optical properties upon the chemical variation and polytypic intergrowth in the Hg-Fe chloritoids has been investigated. The effects of the variation in chemical composition of specific polytypic compositions were analyzed first. The refractive indices of 10 approximately pure 2M₂ Hg-Fe chloritoids show strong correlations (R² ≥ 0.094) to the proportion of Hg cations in the H(1B) site, Hg/(Hg + Fe + Hn) - HGN. Correlations between the optical orientation angles and HGN were weaker (R² ≤ 0.87). The optical orientation is very sensitive to small variations in the polytypic composition, especially orientation angles that have fixed values in 2M₂ chloritoid. The parameter showing the most sensitivity is ∠ X ⋀ b, which is 0° in an ideal 2M₂ chloritoid, but increases to about 6° for a chloritoid containing 10% by volume 1Tc polytype. The sum of ∠ Y ⋀ c* and ∠ Z ⋀ c* for an ideal 2M₂ chloritoid has a value of 90°, whereas a chloritoid with 10% 1Tc has a sum of 92°. Although not as sensitive as ∠ X ⋀ b, this parameter can be determined with only a spindle stage or universal stage. The observed dependence of the optical properties on polytypic intergrowth and chemical variation has been modeled using dielectric tensor calculations based on the properties of a 1Tc layer and assuming that the 2M₂ polytype is derived by twinning the 1Tc polytype about [010] with an (001) composition plane.en
dc.description.degreePh. D.en
dc.format.extentxv, 119 leavesen
dc.format.mimetypeapplication/pdfen
dc.identifier.urihttp://hdl.handle.net/10919/53682en
dc.language.isoen_USen
dc.publisherVirginia Polytechnic Institute and State Universityen
dc.relation.isformatofOCLC# 18161035en
dc.rightsIn Copyrighten
dc.rights.urihttp://rightsstatements.org/vocab/InC/1.0/en
dc.subject.lccLD5655.V856 1988.C666en
dc.subject.lcshPolymorphism (Crystallography)en
dc.titleThe investigation of the optical properties of polytypic mineralsen
dc.typeDissertationen
dc.type.dcmitypeTexten
thesis.degree.disciplineGeological Sciencesen
thesis.degree.grantorVirginia Polytechnic Institute and State Universityen
thesis.degree.leveldoctoralen
thesis.degree.namePh. D.en

Files

Original bundle
Now showing 1 - 1 of 1
Thumbnail Image
Name:
LD5655.V856_1988.C666.pdf
Size:
9.24 MB
Format:
Adobe Portable Document Format
Download

Collections

Doctoral Dissertations