Clifford Frondel

Strontium-Rubidium Age of an Iron Meteorite

The isotopic compositions and concentrations of rubidium and strontium were determined in silicate nodules contained in Weekeroo Station meteorite, a brecciated coarse octahedrite. The strontium had a Sr87:Sr86 range from 0.729 to 0.768, showing considerable enrichment in Sr87 in coinparison with achondrites. Data for six samples of nodules lie on a straight line on the Sr-Rb evolution diagram, with an initial Sr87:Sr86 ratio of 0.696 to 0.702; the slope is 0.0674, corresponding to an age of 4.7 x 109 years for λ = 1.39 x 10-11 year-1. These data agree with the previously assigned ages for the formation of stony meteorites and the earth; they support the conclusion that the major period of chemical and physical differentiation in the solar system occurred in a narrow interval at about this time. This result disagrees with the Ar40-K40 ages of 5 to 13 x 109 years determined from other iron meteorites. A wide variety of isotopic-age investigations now seem experimentally feasible on iron meteorites that contain silicates.

Ureyite, NaCrSi2O6: A New Meteoritic Pyroxene.

The new mineral NaCrSi206 (ureyite) has been found as rareemeraldgreen grains in the iron meteorites Coahuila, Toluca, and Hex River Mountains. X-ray studies of the natural and synthetic material have established that the mineral is isostructural with jadeite, NaAlSi206. Indexed data for powder patterns obtained by x-ray diffraction and precise cell dimensions are given for the Cr, Fe, and Al members of the jadeite group. Unlike jadeite, a high-pressure phase, ureyite can be synthesized from melts at 1-atmosphere pressure.

Meteorites: Optical Activity in Organic Matter

A low- amplitude, positive, Cotton effect, centered at about 340 millimicrons, has been observed in organic extracts of samples from ordinary (noncarbonaceous) chondrites. Ancillary evidence renders it likely that this optical activity derived from contamination by biologic materials on Earth.

Mineralogy and Composition of Lunar Fines and Selected Rocks

Mineralogical descriptions and both wet chemical analyses and microprobe analyses are given of the glasses and crystalline components of the lunar fines and of the minerals in microgabbros (samples 10050 and 10047). The principal minerals described are various clinopyroxenes, plagioclase, olivine, low cristobalite, low tridymite, ilmenite, iron-nickel, iron, schreibersite, cohenite, troilite, and a new CaFe pyroxenoid. Descriptions are given of small craters produced by hypervelocity particle impact on glass and iron-nickel fragments in the fines. The rounding of grains in the fines and of surface rocks is attributed to mechanical ahrasion and not to cratering.

Determination of the Atomic Weight of Silicon by Physical Measurements on Quartz

The value 28.095±0.005 for the atomic weight of silicon has been obtained through precision measurements of the density and unit‐cell volume of an unusually pure crystal of natural quartz, SiO2. The value is based on the Avogadro number, 6.02338, and wavelength conversion factor, 1.002030, of Birge (1945). The following experimental data were obtained: density in g/cc in vacuum at 25°, 2.64847±0.0001; unit‐cell dimensions in kX at 25° and corrected for refraction, a0 4.90360, c0 5.39417, both ±0.0001; indices of refraction for λ589.29 mμ at 18°, nO 1.544258, nE 1.553380, both ±0.00001; inversion temperature 573.3° on both heating and cooling cycles. Direct analysis gave (weight percent): Li2O 0.0005, Na2O 0.0004, K2O 0.0002, Al2O3 0.0008, TiO2 0.0001, MnO2 0.00002, Fe2O3 0.0000. The major systematic errors in this method stem from compositional variation in the quartz, of the nature of a coupled substitution of Al for Si with interstitial (Li,Na), and probably lead to a high value for the atomic weight. F...

Composition of rhodizite

A chemical analysis of rhodizite from Manjaka, Madagascar, establishes the new formula CsAl4Be4B11(OH)4O25. Space group P43m; a0 7.317±0.001 A; density 3.44±0.01 (meas.), 3.47 (calc.); Z=1. The index of refraction, 1.693±0.001 (Na), and the unit cell dimension are identical within the limits state for material from lithia-pegmatites at Manjaka, Antsongombato, Antandrokomby and Ambalalehifotsy, in Madagascar. Hardness 81/2.

Geochemical scavenging of strontium

Crandallite, an abundant mineral belonging to the alunite structure type, is a geochemical host for ordinary strontium in the soil profile and the deeper ground-water circulation. It may be useful in the scavenging or storage of the radioisotopes of strontium and certain other elements.

Strunzite, a New Mineral

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Quartz fibers as templates for biopolymers.

The polymerization of silica in water solution to form quartz fibers proceeds by a dehydration process, analogous to condensation polymerization in organic high-polymers, in which monomeric Si(OH)4 groups unite through Si−O−Si bonds with the elimination of H2O. The resulting fibers are structurally polar along the direction of elongation, are enantiomorphous, and generally shown stereospecific twisting around the direction of elongation. In these regards the fibers are analogues of biopolymers such as RNA and DNA. Quartz also possesses specific adsorptive relations to a wide range of organic substances including monomer amino acids, short-chain polypeptides, and proteins. These involve hydrogen-bonding between (OH) or silanoi groups on the surface of the quartz with active side-groups on the organic molecules and in part are epitaxial through dimensional coincidences in the interface.Geochemical evidence indicates that quartz was deposited in the early Precambrian ocean either by direct crystallization from seawater or by recrystallization of amorphous silica. What is of interest is the possible role of quartz fibers as a template and co-polymer in the passage of biomonomers in the pre-biotic ocean to the long-chain biopolymers such as nucleic acids and proteins that are involved in life processes.