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.