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Dorothy Carroll

Publications and source records attributed to Dorothy Carroll.

9 recordsLinked to original sources
USGS2024

Reactivity of clay minerals with acids and alkalies

One-g samples of a montmorillonite, a metabentonite, an illite, two kaolinites, and three halloysites were treated with 50 ml of hydrochloric acid (6⋅45 N, 1:1), acetic acid (4⋅5 N, 1:3), sodium hydroxide (2⋅8 N), sodium chloride solution (pH 6⋅10; Na = 35‰; Cl = 21⋅5‰), and natural sea water (pH 7⋅85; Na = 35⋅5‰; Cl = 21⋅ 5‰) for a 10-day period in stoppered plastic vials. The supernatant solutions were removed from the clay minerals and analyzed for SiO 2 , Al 2 O 3 , CaO, MgO, Na 2 O, and K 2 O. All the solutions removed some SiO 2 , Al 2 O 3 , and Fe 2 O 3 from the samples, but the quantities were small. Sodium hydroxide attacked the kaolin group minerals more strongly than it did montmorillonite, metabentonite, or illite. Halloysite was more strongly attacked by hydrochloric acid than was any of the other experimental minerals. Hydrochloric acid removed iron oxide coatings from soil clay minerals, but acetic acid did not remove them completely. The samples most strongly attacked by HCl and NaOH were examined by X-ray diffraction. Acid treatment did not destroy the structure of the clays, but the halloysite structure was partially destroyed. Sodium hydroxide attacked the halloysite structure, as shown by chemical analysis and X-ray diffraction. These experiments show that treatment in dilute acids has no harmful effect in the preparation of clays for X-ray diffraction. Acetic acid is preferred to hydrochloric acid for this purpose. Hydrochloric acid cleans clay minerals by removing free iron oxide from the surface; acetic acid is less effective.

Clays and Clay Minerals↗
USGS2006

Sediments from bay St. George, Newfoundland

Sediments cored to a depth of about 1 m in Bay St . George , Newfoundland , were examined for grain‐size distribution and minerals. The sediments are light brown silty clays, the principal minerals of which are chlorite and muscovite mica. The scarce sand consists of fresh detrital grains of blue‐green amphibole, biotite, epidote, zoisite, magnetite, garnet, hypersthene, apatite, chlorite, and scarce zircon. Quartz, plagioclase feldspar, and muscovite are abundant. These minerals are all present in the rocks of the adjacent land areas and have been deposited in the sediments with little alteration or change due to weathering. The clay minerals of the sediments are predominantly muscovite and chlorite with a slight admixture of vermiculite and montmorillonite. There is very little mixed‐layering of these minerals. Montmorillonite may be due to diagenetic changes after deposition of these clays in the marine environment of the bay .

Newfoundland↗
USGS1970

Clay minerals: A guide to their x-ray identification

This paper is a guide to the X-ray examination of clay minerals; it incorporates background information concerning the principal crystallographic features of clay minerals, and how this is used in the X-ray identification of these minerals, together with laboratory techniques and the application of X-ray diffractometry to the diagnosis of the clay minerals in natural sedimentary materials.

Special Papers of the Geological Society of Americ↗
USGS1959

Ion exchange in clays and other minerals

Ion exchange in clays and other minerals is dependent on the crystalline structure of the mineral and on the chemical composition of any solution in contact with the mineral. The structures of clay minerals and zeolites are briefly described to provide a background for the discussion of their ion-exchange reactions. Ion exchange in these minerals is a reversible chemical reaction that takes place between ions held near a mineral surface by unbalanced electrical charges within the mineral framework and ions in a solution in contact with the mineral. Generally the excess charge on the mineral is negative, and it attracts cations from the solution to neutralize this charge. The chemical reactions in ion exchange follow the law of mass action, but the reactions are restricted by the number of exchange sites on the mineral and by the strength of the bonding of the exchangeable cations to the mineral surface. Titration of H-clays with bases shows that montmorillonites and "illites" behave like a mixture of two or three different acids, whereas kaolinite, with an indefinite number of exchange sites, behaves like an indefinite number of acids. Ion-exchange capacity is measured in chemical equivalents of base adsorbed at pH 7. Each clay mineral has a range of exchange capacities because of differences in structure and in chemical composition. The ranges (in milliequivalents per 100 grams) are kaolinite, 3-15; halloysite (2H 2 O), 5-10; halloysite (4H 2 O), 40-50; montmorillonite, 70-100; "illite," 10-40; vermiculite, 100-150; glauconite, 11-20; attapulgite, 20-30; and allophane, 70. The common metallic cations found in exchange positions in clay minerals are Ca +2 , Mg +2 , Na + , and K + . At low pH values H + replaces other cations. The order of replaceability of the common cations has been found to be: Li + < Na + < K + < Rb + < Cs + and Mg +2 < Ca+2 < Sr +2 < Ba +2 Bivalent cations enter the exchange sites preferentially to univalent cations. The common exchangeable cation in most clay minerals in soils is Ca +2 . Other exchange phenomena discussed are anion exchange, fixation of cations and anions by clay minerals, effect of environment on cation exchange, and the exchange capacity of zeolites, of rocks, of other minerals, of organic matter and organic complexes, and of amorphous mineral material.

GSA Bulletin↗