Shattuckite and plancheite: a crystal chemical study

The orthorhombic crystal structures of shattuckite, Cu(5)( SiO(3))(4)(OH)(2) and planchétite, Cu(8)(Si(4)0(11))(2)(OH)(4) H(2)O, have been solved. Shattuckite contains silicate chains similar to pyroxene in a complex association with copper atoms, while the closely related planchéite contains silicate chains similar to amphibole.     

First Natural Occurrence of Coesite

Coesite, the high-pressure polymorph of SiO(2), hitherto known only as a synthetic compound, is identified as an abundant mineral in sheared Coconino sandstone at Meteor Crater, Arizona. This natural occurrence has important bearing on the recognition of meteorite impact craters in quartz-bearing geologic formations.     

Stanfieldite: a new phosphate mineral from stony-iron meteorites

A new mineral, stanfieldite, Ca(4)(Mg,Fe)(5)(PO(4))(6), has been found in the Estherville mesosiderite and several pallasites: Santa Rosalia, Albin, Finmarken, Imilac, Mount Vernon, and Newport. The atom ratio Mg:Fe of this mineral varies from 1.5 in Estherville to a constant ratio of about 15 in the pallasites. X-ray, optical, and chemical data for the mineral resemble those for the only intermediate compound in the system Mg(3)(PO(4))(2)-Ca(3)(PO(4))(2).     

Cubanite: A New Sulfide Phase in CI Meteorites

Cubanite (CuFe(2)S(3)), previously unobserved in meteorites, has been discovered in two carbonaceous chondrites, Orgueil and Alais. The association of this mineral with low-copper pyrrhotite suggests that it formed in a low-temperature environment on the meteorite parent body.     

Carbynes in meteorites: detection, low-temperature origin, and implications for interstellar molecules

Carbon from the Allende meteorite is not graphite but carbyne (triply bonded elemental carbon), inasmuch as on heating to 250 degrees to 330 degrees C it releases mainly triply bonded fragments: -(C identical withC)(n),- with n = 1 to 5, and -(C identical withC)(n)-CN, with n = 1 to 3. Although carbynes have been known to form only by condensation of carbon vapor above 2600 K or by explosive shock of > 600 kilobars, it is found that they also form metastably by the reaction 2CO --> CO(2) + C (solid) at 300 degrees to 400 degrees C in the presence of a chromite catalyst. Such low-temperature formation by surface catalysis may be the dominant source of carbynes on the earth and in meteorites, and a major source of interstellar carbynes and cyanopolyacetylenes.     

Olivine-garnet transformation in a meteorite

Garnet has been identified for the first time as a meteorite mineral in the Coorara chondrite from Western Australia. It replaces olivine grains in a 1-millimeter veinlet traversing the body of the meteorite. The associated olivine has abnormally low birefringence, which suggests a highly shocked condition. Microprobe analyses do not distinguish the garnet from the associated olivine, which has the composition (Mg(.75)Fe(.25))(2) SiO(4); the garnet may have the composition Mg(3)Fe(2)Si(3)O(12) but be unresolvable from the accompanying olivine, or alternatively is nonstoichiometric. Transformation of olivine to garnet under high pressure could have significant implications for the phase composition of the Earth's mantle.     

Pentaborate Polyanion in the Crystal Structure of Ulexite, NaCaB5O6(OH)6{middle dot}5H2O

Triclinic ulexite crystals contain isolated borate polyanions [B(5)O(6)(OH)(6)](3-) related to the well known pentaborate polyanion [B(5)O(6)(OH)(4)](-) by addition of two hydroxyl groups to two opposite B-O triangles. The isolated ulexite polyanions form the [B(5)O(7)(OH)(4)](n)(3n-) chains previously found in crystals of the related mineral probertite, NaCaB(5)O(7)(OH)(4).3H(2)O.     

Exsolution in clinoamphiboles

Ten amphibole specimens from a variety of metamorphic rocks such as talc schists, eclogites, and metamorphosed iron formations contain lamellae of a second amphibole oriented parallel to ([unknown]101) or (100), or both, of the host. Tremolites, actinolites, and hornblendes commonly have lamellae of a calcium-poor clinoamphibole with P2(1)/m space-group symmetry, or lamellae of cummingtonite with C2/m space-group symmetry. Likewise cummingtonites and P2(1)/m clinoamphiboles commonly contain lamellae of calcium-rich C2/m amphiboles such as tremolite. Results of x-ray diffraction, electron-probe, and microscope studies indicate that most lamellae result from unmixing of a homogeneous amphibole. The P2(1)/m clinoamphibole is analogous to the clinopyroxene pigeonite in agreement with the results of M. G. Bown.     

Absence of neutral alkali atoms in rhodizite

The formula CsB(l2)Be(4)Al(4)O(28) has been proposed by others for the mineral rhodizite. Electron-spin-resonance and magnetic susceptibility measurements prove the absence of neutral cesium atoms. An ionic formula CsB(11)Be(4)Al(4)O(26)(OH)(2) is proposed.     

Noble Gases in the Murchison Meteorite: Possible Relics of s-Process Nucleosynthesis

The Murchison carbonaceous chondrite contains a new type of xenon component, enriched by up to 50 percent in five of the nine stable xenon isotopes, mass numbers 128 to 132. This component, comprising 5 x 10(-5) of the total xenon in the meteorite, is released at 1200 degrees to 1600 degrees C from a severely etched mineral fraction, and probably resides in some refractory mineral. Krypton shows a similar but smaller enrichment in the isotopes 80 and 82. Neon and helium released in the same interval also are quite anomalous, being highly enriched in the isotopes 22 and 3. These patterns are strongly suggestive of three nuclear processes believed to take place in red giants: the s process (neutron capture on a slow time scale), helium burning, and hydrogen shell burning. If this interpretation is correct, then primitive meteorites contain yet another kind of alien, presolar material: dust grains ejected from red giants.     

Ammonioborite: new borate polyion and its structure

The mineral ammonioborite is monoclinic with unit cell dimensions (in angstroms): a = 25.27, b = 9.65, and c = 11.56; beta = 94 degrees 17', and the space group is C 2/c. Analysis of the crystal structure revealed the crystallo-chemical formula (NH(4))(3)B(15)O(20)(OH)(8).4H(2)O, with four such formula units in the unit cell. The basic structural unit is the double ring consisting of one BO(4) tetrahedron and four BO(3) triangles: in ammonioborite three of these units are connected to give trimeric ions [B(15)O(20)(OH)(8)](3-).     

Rhenium-osmium isotope systematics of carbonaceous chondrites

Rhenium and osmium concentrations and Os isotopic compositions of eight carbonaceous chondrites, one LL3 ordinary chondrite, and two iron meteorites were determined by resonance ionization mass spectrometry. Iron meteorite (187)Re/(186)Os and (l87)Os/(l86)Os ratios plot on the previously determined iron meteorite isochron, but most chondrite data plot 1 to 2 percent above this meteorite isochron. This suggests either that irons have significantly younger Re-Os closure ages than chondrites or that chondrites were formed from precursor materials with different chemical histories from the precursors of irons. Some samples of Semarkona (LL3) and Murray (C2M) meteorites plot 4 to 6 percent above the iron meteorite isochron, well above the field delineated by other chondrites. Murray may have lost Re by aqueous leaching during its preterrestrial history. Semarkona could have experienced a similar loss of Re, but only slight aqueous alteration is evident in the meteorite. Therefore, the isotopic composition of Semarkona could reflect assembly of isotopically heterogeneous components subsequent to 4.55 billion years ago or Os isotopic heterogeneities in the primordial solar nebula.     

Chondrules: first occurrence in an iron meteorite

Complete chondrules and fragments of chondrules have been found within silicate inclusions from the octahedrite iron meteorite Netschaevo. The bulk chemical composition, mineralogy, and mineral chemistry indicate that this chondritic material has properties intermediate between those of the H-group chondrites and those of the enstatite chondrites.     

Evidence and implications of shock metamorphism in lunar samples

Lunar microbreccias and loose regolith materials contain abundant evidence of shock metamorphism related to crater-forming meteorite impacts. Diagnostic shock effects include (i) planar features in a silica phase and feldspars, and lamellae in clinopyroxene, (ii) thetomorphic feldspar glass, (iii) heterogeneous glasses of rock and mineral composition, (iv) distinctive recrystallization textures, and (v) characteristic changes in crystal structure as indicated by x-ray diffraction analysis and measurements of refractive index. The microbreccias are produced from regolith materials (ejected fromz craters) by shock lithification. Some feldsparrich fragments may represent ejecta introduced from nonlocal sources, such as the lunar highlands.     

对几种典型土壤中粘粒级有机-矿质复合体的初步表征

采用超声分散法提取了江西红壤、黑龙江黑土和北京潮土等3种典型土壤的粘粒级有机-矿质复合体,分别用傅立叶转换红外光谱(FTIR)、X射线衍射(XRD)、扫描电镜-X射线能谱(SEM-EDS)以及固态核磁共振(NMR)等方法对提取的有机-矿质复合体进行了表征。结果表明,黑土复合体具有最高的有机质含量和最大的阳离子交换容量。3种复合体的主要矿物成分均为石英,但红壤复合体还含有云母与闪石等成分,而黑土和潮土复合体主要还包括长石和方解石成分。对NMR不同化学位移域的谱峰积分得到3种粘粒级复合体有机碳的组成比例,红壤复合体中脂类C的含量最高,黑土复合体中烷氧基C的含量最高,而潮土中烷氧基C、脂类C以及芳香族C的含量相差不多。     

Charge distribution in the light-atom mineral kernite

A charge density analysis of accurate x-ray data for the mineral kernite Na(2)B(4)O(6)(OH)(2). 3H(2)O indicates that the sodium and boron atoms have partial positive charges of 0.4 to 0.5 unit and 0.4 to 0.7 unit, respectively, whereas the oxygen atoms have negative charges of about 0.4 to 0.5 unit. The best agreement with the intensities and with the experimental scale factor is obtained with contracted molecule-optimized atomic orbitals. Difference density maps based on high-order parameters show more density in B-O than in Na-O bonds, thus supporting the covalent nature of the bonds between boron and oxygen atoms.     

Pecoraite, Ni6Si4O10(OH)8, Nickel Analog of Clinochrysotile, Formed in the Wolf Creek Meteorite

Pecoraite is a new phase in the natural system H(2)O-NiO-MgOSiO(2), the nickel analog of clinochrysotile. It occurs in cracks in the Wolf Creek meteorite in Australia where it was formed under hydrothermal conditions. Particles of pecoraite are very small curved plates which have begun to coil; some have achieved spiral form.     

The Tagish Lake meteorite: a possible sample from a D-type asteroid

A new type of carbonaceous chondrite, the Tagish Lake meteorite, exhibits a reflectance spectrum similar to spectra observed from the D-type asteroids, which are relatively abundant in the outer solar system beyond the main asteroid belt and have been inferred to be more primitive than any known meteorite. Until the Tagish Lake fall, these asteroids had no analog in the meteorite collections. The Tagish Lake meteorite is a carbon-rich (4 to 5 weight %), aqueously altered carbonaceous chondrite and contains high concentrations of presolar grains and carbonate minerals, which is consistent with the expectation that the D-type asteroids were originally made of primitive materials and did not experience any extensive heating.     

Opaque minerals of the lunar rocks and dust from mare tranquillitatis

The opaque minerals in the lunar rocks 10047, 10050, 10057, 10059, 10068 and in the dust were studied. Rock 10047 contains ilmenite as a main component besides Al-bearing chromian ulv?spinel, a new Ti, Fe, Zr, Y, Ca silicate, troilite, cobaltian alpha Fe, minor hafnian baddeleyite and dysanalyte. Dysanalyte contains Ca, Ti, and Fe as major elements and shows concentrations (rare earth elements together approximately 10 percent) of La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Hf, Y, and Zr plus traces of Nb, Ba, and Na. The chemistry of ilmenite in the igneous rocks shows no appreciable variations. A new mineral of the solid solution series MgTi(2)O(5)-FeTi(2)O(5) has also been encountered in the polymict breccias. The microbreccias and the fines contain meteorite debris indicating an impact origin.     

A major meteorite impact on the Earth 65 million years ago: evidence from the cretaceous-tertiary boundary clay

Evidence for a major meteorite impact on the earth 65 million years ago is shown by the presence of meteoritic debris in the "fish clay" from Denmark representing the Cretaceous-Tertiary boundary. Noble metals (iridium, osmium, gold, platinum, rhenium, ruthenium, palladium, nickel, and cobalt), which are sensitive indicators of meteorites and are normally depleted on the terrestrial surface by factors of 10(4) to 10(2) relative to cosmic abundances, are enriched in this boundary clay by factors of 5 to 100 over the expected abundances. With the exception of rhenium, all the enriched noble metals in the clay are present in cosmic proportions, indicating that the impacting celestial body had not undergone gross chemical differentiation. The major extinction of life on the earth at the end of the Cretaceous Period may be related to the meteorite impact.