Search USGS⌕ Search

SEARCH · Search USGS

Results for “American Mineralogist”

Search indexed USGS publications on groundwater, aquifers, geologic maps, mineral resources and earthquakes. Explore source records by subject and place.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 91 records · Page 5Linked to original sources
USGS1982

Margaritasite: a new mineral of hydrothermal origin from the Pena Blanca uranium district, Mexico.

Margaritasite, (Cs,K,H3O)2(UO2)2V2O8.nH2O (where Cs > K, H3O and n approx 1), a 10.514, b 8.425, c 7.25 A, beta 106.01o, P21/a, Z = 2, is a newly recognized uranium ore mineral named for the Margaritas deposit, Pena Blanca uranium district, Chihuahua, Mexico, at which it was discovered. A Cs-rich analogue of carnotite, margaritasite is the natural equivalent of synthetic Cs-uranyl vanadate (A.M. 43- 799, 50-825). A fine-grained yellow mineral, it is most easily distinguished from carnotite by XRD; X-ray powder patterns (CuKalpha radiation) show that the (001) reflection of margaritasite lies at 12.7o (2theta ), while that of carnotite is found at 13.8o (2theta ). The shift of the (001) reflection in margaritasite reflects the structural changes caused when Cs occupies the sites filled by K in carnotite. Synthesis experiments indicate that margaritasite also differs from carnotite in a higher-T hydrothermal origin. Chemical analyses and XRD data for margaritasite and synthetic Cs- carnotite, and chemical analyses for rocks from Sierra Pena Blanca and vicinity, are tabulated.-J.A.Z.

American Mineralogist↗
USGS1985

Electronic spectra of Fe3+ oxides and oxide hydroxides in the near IR to near UV.

Optical absorption and diffuse reflectance spectra of several Fe2O3 and FeOOH polymorphs (hematite, maghemite, goethite, lepidocrocite) in the near-IR to near-UV spectral regions (2000-200 nm) are presented. The spectra consist primarily of Fe3+ ligand field and ligand-to-metal charge-transfer transitions.-J.A.Z.

American Mineralogist↗
USGS1985

Dissolution of olivine in basaltic liquids: experimental observations and applications.

Rates of olivine dissolution in synthetic lunar basalt 77115 and a silica-enriched 77115 composition (Sil-77115) at superliquidus temperatures have been determined. Dissolution-rate data have been applied to the problem of the thermal history of fragment-laden impact-melt rocks of the lunar highlands. Textural and chemical criteria are discussed for the recognition of olivine resorption (and growth) phenomena in igneous rocks. -J.A.Z.

American Mineralogist↗
USGS1985

Geology of the Silsilah ring complex, and associated tin mineralization, Kingdom of Saudi Arabia - a synopsis.

A tin greisen deposit is associated with an alkali-feldspar granite that forms part of a ring complex at Jabal as Silsilah. The petrological and geochemical characteristics of the Fawwarah alkali-feldspar granite resemble those of granites located elsewhere that are also associated with deposits of Sn, W and rare metals. The alkali-feldspar granite is peraluminous, incompatible trace-element-enriched, and is characterized by a flat chondrite-normalized REE pattern that includes a very large, negative Eu anomaly. The distinctive mineralogy of the alkali-feldspar granite includes zinnwaldite and topaz. Differentiation and mineral fractionation controlled magma evolution while components of the ring complex were sequentially emplaced. Evolution of the ring complex and its associated tin deposit concluded with local, intense alteration of the Fawwarah alkali-feldspar granite to a cassiterite-bearing greisen. Samples of greisens suggest that the locus of economic tin deposits is not restricted to the two known, strongly mineralized greisens.-J.A.Z.

American Mineralogist↗
USGS1985

Metasomatism, titanian acmite, and alkali amphiboles in lithic- wacke inclusions within the Coyote Peak diatreme, Humboldt County, California.

Lithic-wacke inclusions within the alkali-ultramafic diatreme at Coyote Peak record a history of pronounced metasomatism and crystal growth. The dominant metasomatic changes were loss of Si from the inclusions and mass influx of K, due to an unusually high K activity in the ultramafic host. The reaction with K converted much of the clay, quartz and lithic fraction of the lithic wacke into microcline, and exchanged Na from abundant clastic albite. Probe analyses are tabulated for cores and rims of titanian acmites, augites and alkali amphiboles. -J.A.Z.

American Mineralogist↗
USGS1984

Santaclaraite, a new calcium-manganese silicate hydrate from California.

Santaclaraite, ideally CaMn4(Si5O14(OH))(OH).H2O, occurs as pink and tan veins and masses in Franciscan chert in the Diablo Range, Santa Clara and Stanislaus counties, California. It is associated with four unidentified Mn silicates, Mn-howieite, quartz, braunite, calcite, rhodochrosite, kutnahorite, baryte, harmotome, chalcopyrite and native copper. Santaclaraite is triclinic, space group B1, a 15.633(1), b 7.603(1) , c 12.003(1) A, alpha 109.71(1)o, beta 88.61(1)o, gamma 99.95(1) o, V 1322.0(3) A3; Z = 4. The strongest lines of the X-ray pattern are 7.04(100), 3.003(84), 3.152(80), 7.69(63), 3.847(57) A. Crystals are lamellar to prismatic (flattened on (100)), with good cleavage on (100) and (010); H. 61/2 Dcalc. 3.398 g/cm3, Dmeas. 3.31 (+ or -0.01); optically biaxial negative, alpha 1.681, beta 1.696, gamma 1.708 (all + or - 0.002), 2Valpha 83 (+ or -1)o. Although chemically a hydrated rhodonite, santaclaraite dehydrates to Mn-bustamite at approx 550oC (in air) . Santaclaraite is a five-tetrahedral-repeat single-chain silicate and has structural affinities with rhodonite, nambulite, marsturite, babingtonite and inesite.-J.A.Z.

American Mineralogist↗
USGS1985

An oxygen buffer for some peraluminous granites and metamorphic rocks.

The mineral assemblage biotite-garnet-muscovite-magnetite-quartz and its sub-sets are common in many peraluminous granites, schists and gneisses. If the biotite and garnet are reasonably iron-rich, then the system is a useful buffer for fO2. Available thermochemical data indicate that, in T-fO2 space, the buffer curve is located between the hematite-magnetite curve and the quartz-magnetite-fayalite curve, in a region that previously had no buffer curve applicable to peraluminous rocks. -J.A.Z.

American Mineralogist↗
USGS1984

New data for iimoriite.

In its first reported occurrence outside of Japan, iimoriite, Y2(SiO4)(CO3), has been found in a thorite- and uraninite-bearing quartz and albite vein from Bokan Mountain on Prince of Wales Island, Alaska. It occurs as buff-tan subhedral and anhedral grains, 0.01-0.5 mm in diameter, with vitreous lustre, white streak, and H. 51/2-6. Colourless in thin section, with no pleochroism, iimoriite is biaxially negative with alpha 1.753, beta 1.824, gamma 1.830, 2Valpha (obs.) 31o, 2Valpha (calc.) 31.5o. The mineral is triclinic, space group P1 or P1, a 6.573(1), b 6.651(1), c 6.454(1) A, alpha 116.44, beta 92.34, gamma 95.63o, Z = 2, Dobs. 4.47, Dcalc. 4.56 (from Gladstone-Dale relationship), Dcalc. 4.91 (from calculated formula weight and cell volume) g/cm3. The strongest XRD lines are 2.88(100), 2.95(80), 2.78(40), 3.02(36), 2.84(35) A. Chemical analyses are tabulated. -J.A.Z.

American Mineralogist↗
USGS1984

Heat capacity and thermodynamic functions for gehlenite and staurolite: with comments on the Schootky anomaly in the heat capacity of staurolite.

The heat capacities of a synthetic gehlenite and a natural staurolite were measured from 12 and 5 K, respectively, to 370 K by adiabatic calorimetry, and the heat capacities of staurolite were measured to 900 K by differential scanning calorimetry. At 298.15 K and 1 bar the entropy of gehlenite is 210.1 + or - 0.6 J/(mol.K) and that of staurolite is 1019.6 + or - 12.0 for H2Al2Fe4Al16Si8O48 and 1101.0 + or - 12.0 for 103(H3Al1.15Fe2+0.60)- 324(Fe2+2.07Fe3+0.54 Ti0.08Mn0.02Al1.19)(Mg0.44Al15.26)Si8O48. -J.A.Z.

American Mineralogist↗
USGS1984

The fluids in salt.

The characteristics of fluid inclusions in salt, the geological processes through which these fluids evolve, and the possible problems such inclusions pose for nuclear waste disposal in salt beds or domes are reviewed.-J.A.Z.

American Mineralogist↗