Showing papers on "Silicate minerals published in 1968"
01 Jan 1968
TL;DR: In this paper, the physical properties, chemistry, and areal distribution of those silicate minerals that formed in the tuffs during diagenesis of Lake Tecopa were summarized.
Abstract: '!'he deposits of Pleistocene Lake Tecopa cover about 90 square miles along the Amargosa River in southeastern Inyo Co'unty. These deposits consist chiefly of mudstone and interbe~ded rhyolitic vitric tuffs that interfinger marginward with co~rser clastic sediments. A total of 12 tuffs, 2 inches to 13 fet=tt thick, were recognized in the 220 feet of exposed section. Tliey are mainly the result of ash falls directly into the lake, although the upper parts of some contain reworked material. This report summarizes the physical properties, chemistry, and areal distribution of those silicate minerals that formed in the tuffs during diagenesis. Zeolites, monoclinic potassium feldspar, searlesite, clay minerals, and opal occur in the altered tuffs. The zeolites are mainly phillipsite, clinoptilolite, erionite, and in trace to minor amounts, analcime and chabazite. Clay minerals are nearly ubiquitous and occur in trace to major amounts associated chiefly with zeolites and potassium feldspar. Most beds contain two or more zeolites, but some beds are monomineralic. Potassium feldspar also locally forms monomineralic beds. Zeolites are locally associated with relict glass; potasssium feldspar and searlesite are locally associated with zeolites, but nowhere has potassium feldspar oc searteslite been round associated with relict glass. Textural evidence shows that some po•tassium feldspar and searlesite replace phillipsite and suggests that all potassium feldspar and searlesite in the tuffs formed from phillipsite and other early diagenetic zeolites rather than directly from the rhyolitic glass. Three diagenetic facies recognized in the tuffs have fresh glass, zeolite, and potassium feldspar or searlesite as their diagnostic constituents. The fresh-glass facies is alrong the lake margin and is succeeded basinward by the zeolite facies and then by the potassium feldspar facies in the central part of the basin. The boundary between the zeolite and potassium feldspar facies bulges basinward at the inlets to Lake Tecopa. Original textures and sedimentary structures are generally preserved in tuffs of the zeolite and potassium feldspar facies. Preservation of these features in altered tuffs that are laterally equivalent to tuffs of the fresh-glass facies is convincing evidence that the present differences in composition and mineralogy are due to postdepositional processes. Experimental work by other mineralogists indicates that the formation of zeolites and feldspar is favored over clay minerals by a relatively high alkali ion to hydrogen ion activity ratio. The distribution and the gradational character of the facies are undoubtedly due to a chemical zonation of the pore water during diagenesis. The pore water was "fres'h" near the margin and inlets of the lake but increasingly alkaline and saline bas:inward. This zonation was probably inherited from the depositional environment. Water of Lake Tecopa was probably moderately to highly saline with a pH of 9 or higher, except near the lake margin. Solution of the 'rhyolitic glass by alkaline and saline pore water provided the material necessary for formation of zeolites and, subsequently, potassium feldRpar. The paragenesis of silicate minerals within the zeolite facies is attributed to variations in the Na+ +K+: H+ activity ratio, the activity of H20, the activity of Si02 and the K: Na+Ca+Mg ratio in the pore
169 citations
TL;DR: In this article, the losses of dissolved Ca, Na, Mg and K have been determined for six small watersheds in New Hampshire during the period 1963-1967, from the rate at which Ca and Na are lost, the steady-state chemical weathering rate is calculated at 800 kg of bedrock-till per hectare per year.
165 citations
01 Jan 1968
TL;DR: In this article, it was shown that the oxidation of benzidine to benzidine-blue on silicate minerals occurs at aluminium atoms exposed at crystal edges and at transition metal atoms in the higher valency state present in the silicate lattices.
Abstract: The oxidation of benzidine to benzidine-blue on silicate minerals is shown to occur at aluminium atoms exposed at crystal edges and at transition metal atoms in the higher valency state present in the silicate lattices. The transition metals in the silicate lattice undergo chemical oxidation-reduction reactions. Changes in the colour of the benzidine-blue radical cation with the conditions of reaction are discussed in terms of the solvent used for the reaction and its influence on the pH of the mineral surface.
51 citations
TL;DR: The unpolarized optical absorption spectra of the sheet silicate minerals muscovite, lepidolite, and fuchsite have been examined in this article, interpreted on the basis of ligand field theory.
Abstract: The unpolarized optical absorption spectra of the sheet silicate minerals muscovite, lepidolite, and fuchsite have been examined. The spectra, interpreted on the basis of ligand field theory, indic...
39 citations
Journal Article•
36 citations
TL;DR: In this paper, the authors considered that the infrequent occurrence of pyrophyllite in more evolved sedimentary rocks and low grade metamorphic facies of pelitic rocks is due to chemical controls in the bulk composition of these rocks.
Abstract: The infrequent occurrence of kaolinite and especially of pyrophyllite in more evolved sedimentary rocks and low grade metamorphic facies of pelitic rocks is considered to be due to chemical controls in the bulk composition of these rocks. Hydrogen-rich organic gases are released from the original sedimentary organic materials during diagenesis and early metamorphism. These gases in turn reduce the iron present from the ferric to ferrous state. The effect of the valence change of the iron is to shift its position in the silicate minerals present. As a result, aluminum is obliged to readjust to the new conditions moving from an alumino-silicate phase to the mica and perhaps the chlorite phases. The new assemblage does not contain a hydrous alumino-silicate though both kaolinite and pyrophyllite could be stable in the physical environment of the rocks.
18 citations
TL;DR: In glacial marine sediments from the St. Lawrence estuary, iron varies between 1.32 and 5.42%, manganese between 0.043 and 0.28%, and titanium around 0.64%.
Abstract: In glacial marine sediments from the St. Lawrence estuary, iron varies between 1.32 and 5.42%, manganese between 0.043 and 0.28%, and titanium between 0.31 and 0.64%. The regional distributions of these elements are related to sediment texture. Analyses of individual sediment size-fractions show that Fe, Mn, and Ti concentrations generally increase with decreasing grain size. Variations in elemental ratios between the different grades suggests that not all of the Fe and Mn is located in detrital silicate minerals. Dithionite extraction of selected sediments resulted in preferential dissolution of 3–16% of the total iron, presumably that derived from amorphous and crystalline iron oxides and from sorbed material.Hydroxylamine–hydrochloride removed 5–60% of the total manganese, presumably that derived from exchangeable Mn, easily reducible Mn oxides, and sorbed Mn material. The soluble fraction is highest in freshly deposited pelites from the center of the estuary. Soluble Fe and Mn occur as oxide films on ...
18 citations
15 citations
TL;DR: In this article, the authors measured the Mossbauer spectra for sixteen samples of natural minerals, including siderite, vivianite, garnets, olivines, pyroxenes, and other silicate minerals.
Abstract: The Mossbauer spectra have been measured for sixteen samples of natural minerals, including siderite, vivianite, garnets, olivines, pyroxenes, and other silicate minerals, The spectra were analyzed for the isomer shifts and quadrupole splittings, and the information thus obtained was correlated with the oxidation states of irons and the crystal structure of minerals. The relative abundances of the various sites present in a given mineral were also estimated by measuring the relative intensities of the absorption peaks in the resolved spectrum of the mineral. All the basic Mossbauer spectral patterns observed for the natural minerals are presented in graphic form.
10 citations
8 citations
TL;DR: In this article, the authors used Sephadex G-10 to isolate sodium alizarin sulphonate from commercial samples of Alizarin Red S that contained variable and large amounts of inorganic salts.
Abstract: Sephadex G-10 has been used to isolate sodium alizarin sulphonate from commercial samples of Alizarin Red S that contained variable and large amounts of inorganic salts. Aluminium in silicate minerals can be reliably determined with the purified reagent, which gives a linear response up to 180 µg of aluminium.
TL;DR: The clay mineralogy of sediments from the Taku estuary was characterized employing 35 clay samples, eighteen of which were fractionated with the supercentrifuge to obtain mineralogical details not available from diffraction patterns of bulk clay (< 2 μ) samples as discussed by the authors.
01 Apr 1968
TL;DR: The occurrence of some nickel silicate minerals as encrustations along joint planes and shear zones of the chromite bearing ultrabasic rocks of Nuggihalli schist belt is described in this paper.
Abstract: The occurrence of some nickel silicate minerals as encrustations along joint planes and shear zones of the chromite bearing ultrabasic rocks of Nuggihalli schist belt is described Chemical and X-ray study shows besides amorphous nickel silicate, the presence of granierite, nepouite or nickel antigorite The nickel minerals are secondary developed by the action of circulating waters The source of nickel is olivine, in the structure of which Ni is known to be present, either as camouflaged or captured ion