Up to three sequential 3‐day treatments with commercial H2SiF6 were required to remove feldspar XRD peaks from many samples of loess and glacial till. Two such repeated treatments lowered the yield of isolated quartz by about 10%. For example, with Memphis C horizon loess from Yalobusha Co., Miss., the yield dropped from 29 to 19% of the 1–10 µm size fraction. Pretreatment of the H2SiF6 with finely ground quartz (1–100 µm size fraction) raised the quartz yield after one or two 3‐day treatments about 10%, for example from 29 to 39% of the initial 1–10 µm fraction of Yalobusha loess. After a third 3‐day treatment the yield was 32%. The quartz of this loess was of 100% purity after one 3‐day H2SiF6 treatment, as established by XRD and XRS. The oxygen isotope delta value was affected a little, the δ18O declining from 17 to 16‰ for the 1–10 µm quartz isolates treated one to three times with H2 SiF6, and fine quartz particles were released (SEM) from clusters in fine chert contained in the loess.

Abstract--Hexafluorotitanic acid (H2TiF6) selectively dissolves kaolinite and most other phyllosilicate minerals of soils and sediments, concentrating free crystalline (Ti, Fe)O2 minerals (partially substituted anatase and rutile) in the residue. A series of H2TiF6 reagents was standardized by analysis of the Ti content and by tests with pure anatase and commercial kaolinites. The Ti in the H2TiF6 solution selected (made from 49% HF + reagent TiO2) was 16.5% by weight as analyzed by the Tiron method. Treatment of pure anatase with the reagent H2TiF6 resulted in a 98% by weight recovery of TiO2 in the residue. The fraction of TiO2 recovered in the residue of commercial Georgia kaolinites was 88-101}/o after treatment with the selected H2TiF6 reagent. Isolates from nine Georgia kaolinite samples with varying amounts of TiOz and Fe203 were examined by X-ray powder diffraction, scanning electron microscopy and elemental analysis. The main constituent of the (Ti,Fe)O2 isolates was anatase for all samples, with minor amounts of coarser rutile and mica from coarser kaolinite. The anatase and rutile isolates contained 74-93% (Ti,Fe)O~ with 0-5-3-1% Fe. The other constituents of the isolates were muscovite of mica (0"3-7~o), quartz (0-9~o) and amorphous relics of vermiculite and/or kaolinite (6-19%). Rutile, muscovite and quartz appear to be detrital but the anatase and relics are probably authigenic. Fine anatase appears to stick on the muscovite flakes as revealed by scanning electron microscopy and heavy liquid data for separation of these two minerals. The (Ti,Fe)Oz isolates from kaolinites which passed with the first magnetic concentrate of anatase were coarse, on the order of a few microns dia., as revealed by the scanning electron microscopy. Those passed with subsequent extensive magnetic concentrates from the same samples were finer. The anatase isolated from kaolinite purified by removal of as much of the impurities as possible by magnetic means was extremely fine, most of the particles being on the order of 0.1 #m dia. More than one third of the total FezO 3 in kaolinites magnetically separated in the first pass was extracted by the citrate-bicarbonate-dithionite treatment after hot NaOH dissolution of 5~74% of the kaolinite, showing that the Fe203 had been mainly associated within the kaolinite. Only 2-6% of the total Fe203 was extracted from magnetically purified kaolinite after 40-50~o of this kaolinite had been dissolved, indicating that most of the Fe is in the anatase and futile fraction.

The ferrous iron content of two vermiculitized biotites decreased by treatment with 0.1 N salts of copper at 70~ from 9.1-14% to 1.8-2.6%. Presumably, interlayer copper ions acted as a catalyst (here, an electron carrier) for the oxidation of iron by dissolved oxygen. The oxidized iron was ejected from the structure and formed crystalline iron minerals, such as hematite and goethite. Weight loss determinations, chemical, and X-ray powder diffraction data suggest that Cu(II) ions were polymerized to hydroxy-hydrous compounds in the interlayer space. Poor exchangeability of the resultant complex is attributed to the formation of strong electrostatic attractions between OH groups of the interlayer complexes and silicate oxygens.

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Abstract--Quartz isolated from soils by the pyrosulfate-H2SiF6 method and chert samples of various origins were examined with the scanning electron microscope. Quartz isolates of the 20-50 #m from the A2 and B21t horizons of the Baxter soil (AR), with quartz 6180 of 18"2 and 19.0~ respectively, showed a mixture of detrital quartz particles and chert clusters of aggregates of fine euhedral quartz crystals. The ~5 pm fractions of both horizons consisted mainly of euhedral quartz particles. The 21~50 #m fraction from the underlying chert, with a 6 ~ 50 = 29.6%~ consisted of aggregates of euhedral quartz particles 1 10#m diz/'; and of subhedral particles 0.1-0.5#m dia. In the soil fractions, the size and shape of the quartz particles as well as oxygen isotope data indicated that the aggregates were from the underlying chert but that irregular, unaggregated grains were detritally admixed loess, particularly in the medium and coarse silt fractions. This mixing of chert (of low temperature origin and heavy oxygen) with detrital quartz (of high temperature origin and light oxygen) gave rise to the intermediate 6180 values in the soil quartz. The SEM of cherts of different geological ages showed different morphologies. Prismatic, polyhedral microcrystalline quartz of 1-10 #m size as well as submicton, euhedral particles were observed in cavities. Submicron, subhedral particles and interlocking quartz grains were characteristic of Precambrian chert. Quartz grains more than 100 #m in size isolated by HC1 from Ordovician dolomite (WI) had large (many microns) subhedral overgrowths and attached clusters of 0.1-0.5 #m microcrystalline quartz. A Danish flint formed in chalk had calcite-lined cavities (x-ray emission determined) in which spheroidal fibrous chalcedony occurred.