Ti-bearing phases in the Huber Formation, an east Georgia kaolin deposit

Citation
Pa. Schroeder et J. Shiflet, Ti-bearing phases in the Huber Formation, an east Georgia kaolin deposit, CLAY CLAY M, 48(2), 2000, pp. 151-158
Citations number
27
Categorie Soggetti
Environment/Ecology,"Earth Sciences
Journal title
CLAYS AND CLAY MINERALS
ISSN journal
00098604 → ACNP
Volume
48
Issue
2
Year of publication
2000
Pages
151 - 158
Database
ISI
SICI code
0009-8604(200004)48:2<151:TPITHF>2.0.ZU;2-D
Abstract
Six kaolin samples from the Lower Tertiary Huber Formation near Wrens, Geor gia were analyzed using transmission electron microscopy (TEM), electron di ffraction (ED), powder X-ray diffraction (XRD), chemical analysis, and magn etic susceptibility to characterize the Ti-bearing phases. Selected samples were treated with 5 M NaOH to remove kaolinite and concentrate the Ti-bear ing phases for additional analysis. TiO2 content in the bulk fraction range s from 1.2 to 5.4 wt. %. There are at least three Ti-bearing phases, includ ing anatase, rutile, and a poorly defined nanocrystalline form. Anatase is most abundant and is commonly found with {010} faces in association with ka olinite edge and basal faces. The nanocrystalline form occurs at 0-1 wt. %, and rutile occurs in trace amounts. Bulk XRD analysis correlates well with the bulk TiO2 chemical measurements. Average anatase unit-cell parameters are a = 0.37908 +/- 0.0002 nm and c = 0.951 +/- 0.001 nm. These parameters indicate an approximate chemical formula of Fe0.053+Ti0.954+O1.95(OH)(0.05) . The distribution of TiO2 content as a function of depth may be useful to ob tain original grain-size variations associated with relative sea-level chan ges responsible for the deposition of the Huber Formation. Evidence for ori ginal depositional sediment properties can be seen in the occurrence of pse udomorphic replacement of micas and fecal pellets by kaolinite. Additional evidence for post-depositional changes includes the sub-micrometer euhedral character and low Fe content of the anatase (relative to soil-derived anat ase). These observations for the Huber Formation are consistent with a prev iously published theory for kaolin genesis that includes biomineralization of originally coarser-grained aluminosilicates into a kaolinite-rich ore bo dy.