Article

Analysis and chemical composition of larnite-rich ultrarefractory materials

Centro de Astrobiologı́a (CSIC/INTA), Instituto Nacional de Tecnica Aeroespacial, Ctra de Ajalvir, km 4, 28850 Torrejón de Ardoz, Spain; Departamento de Geologı́a, Museo Nacional de Ciencias Naturales, CSIC, Madrid, Spain; ISOTRACE Laboratory, University of Toronto, 60 St. George Street, Toronto, Ont., Canada M5S 1A7; Laboratorio de Isótopos Estables, Estación Experimental del Zaidı́n, CSIC, Profesor Albareda 1, 18008 Granada, Spain; Department of Geology, University of Toronto, Toronto, Ont., Canada M5S 3B1; Department of Chemistry, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093, USA
Journal of Materials Processing Technology 04/2004; 147(2):204-210. DOI: 10.1016/j.jmatprotec.2003.11.036

ABSTRACT Larnite (b-Ca2SiO4) is a rare, little known compound. However, despite its scarcity, larnite is found in different natural settings, almost always under thermodynamic conditions of around 0.2–1 kbar and 1000–1100 °C. Larnite can also be formed artificially, especially during the synthesis of high technology refractory and ceramic materials, and as a mineral component of some industrial slags and portland cements. This work describes the analysis and compositional properties of larnite-rich ultrarefractory materials, cataloged as possible meteorite specimens, from the collection of the “Museo Nacional de Ciencias Naturales” (Madrid). Larnite is associated with metal oxides and sulfides, native iron and copper, and calcium-aluminium silicates. Bulk chemical composition was determined by XRF (specific standards and analytical routines were designed). Minor and trace elements (including rare earths) were analyzed by the combination of INAA, ICP-MS and ICP-AES. Larnite occurs as imperfectly developed tabular crystals, mainly displaying rhombic shapes of around 25 mm × 35 mm. SEM and microprobe analyses indicate its chemical composition closely matches the theoretical formula (x=Ca1.96Si0.98O4), although significant amounts of Al (Al0.19–Al0.54), Fe (Fe0.01–Fe0.14), Mn (Mn0.01–Mn0.03) and Mg (Mg0.01–Mg0.02) have also been detected in some crystals. PIXE analyses display high Fe and Ba values, ranging from 3.9 to 8.4 wt.%, and from 1058 to 1530 ppm, respectively.

0 Bookmarks
 · 
151 Views
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The Eocene volcanic suite of the Freemans Cove area of Bathurst Island, Canadian Arctic Archipelago, consists of dikes, sills, small plugs, and agglomeratic vents. Lavas are preserved only as clasts in the vents. The bulk of the magmatism consists of nephelinite or larnite-normative nephelinites and basanites. Subordinate members of the suite include olivine melilite nephelinites, phonolites, and tholeiitic and alkali basalts. The magmatism is bimodal and intermediate rocks are absent. Many of the nephelinites and basanites have the geochemical characteristics of primary magmas, and it is proposed that these members of the suite represent an integrated series of primary melts erupted in an essentially unmodified state from the upper mantle. Other members of the suite are generated by the combined effects of high- and low-pressure differentiation of the primary melts. The igneous rocks are confined to the grabenlike Southeast Bathurst Fault Zone and were emplaced during uplift and compression of the region by the Eurekan rifting episode. The magmatism has the petrological characteristics of intraplate continental magmatism of the type commonly associated with rifting and doming.
    Canadian Journal of Earth Sciences 02/2011; 21(4):428-436. · 1.37 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Perovskite and melilite crystals from melilitolites of the ultramafic alkaline Gardiner complex (East Greenland) contain crystallised melt inclusions derived from: (1) melilitite; (2) low-alkali carbonatite; (3) natrocarbonatite. The melilitite inclusion (1) homogenisation temperature of 1060 °C is similar to liquidus temperatures of experimentally investigated natural melilitites. The compositions are peralkaline, low in MgO (ca.␣5 wt%), Ni and Cr, and they are low-pressure fractionates of more magnesian larnite-normative ultramafic lamprophyre-type melts of primary mantle origin. Low-alkali carbonatite compositions (2) homogenise at 1060–1030 °C and are compositionally similar to immiscible calcite carbonatite dykes derived from the melilitolite magma. Natrocarbonatite inclusions (3) homogenise between 1030 and 900 °C and are compositionally similar to natrocarbonatite lava from Oldoinyo Lengai. Nephelinitic to phonolitic dykes which are related to the calcite carbonatite dykes, are very Zr-rich and agpaitic (molecular Na2O + K2O/Al2O3 > 1.2) and resemble nephelinites of Oldoinyo Lengai. The petrographic, geochemical and temporal relationships indicate unmixing of carbonatite compositions (ca. 10% alkalies) from evolving melilitite melt and continued fractionation of melilitite to nephelinite. It is suggested that the natrocarbonatite compositions represent degassed supercritical high temperature fluid formed in a cooling body of strongly larnite-normative nephelinite or evolved melilitite. The Gardiner complex and similar melilitolite and carbonatite-bearing ultramafic alkaline complexes are believed to represent subvolcanic complexes formed beneath volcanoes comparable to Oldoinyo Lengai and that the suggested origin of natrocarbonatite may be applied to natrocarbonatites of Oldoinyo Lengai.
    Contributions to Mineralogy and Petrology 01/1997; 126(4):331-344. · 3.48 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Acid rain from the Cretaceous-Tertiary (K-T) boundary impact event should have caused significant damage to freshwater life, but only minor extinctions of freshwater species are actually observed. We propose a mechanism to neutralize the acid using larnite (beta-Ca2SiO4), produced as a result of the specific lithology at the Chicxulub impact site. The impact vapor plume must have been enriched in calcium from the carbonate-rich target, leading to the crystallization of larnite. The acid-neutralizing capacity of the larnite grains would have been high enough to consume acid produced after the K-T event within several hours, reducing it to a level at which freshwater life would not have been affected, even if all the acid had precipitated instantaneously after the K-T impact. This scenario can explain some of the extinction selectivity at the K-T boundary.
    Geology. 01/2003; 31(6).

Full-text (2 Sources)

View
153 Downloads
Available from
May 21, 2014