Rocks carbonaceous

Percentage of meteorites seen to fall. Chondrites. Over 90% of meteorites that are observed to fall out of the sky are classified as chondrites, samples that are distinguished from terrestrial rocks in many ways (3). One of the most fundamental is age. Like most meteorites, chondrites have formation ages close to 4.55 Gyr. Elemental composition is also a property that distinguishes chondrites from all other terrestrial and extraterrestrial samples. Chondrites basically have undifferentiated elemental compositions for most nonvolatile elements and match solar abundances except for moderately volatile elements. The most compositionaHy primitive chondrites are members of the type 1 carbonaceous (Cl) class. The analyses of the small number of existing samples of this rare class most closely match estimates of solar compositions (5) and in fact are primary source solar or cosmic abundances data for the elements that cannot be accurately determined by analysis of lines in the solar spectmm (Table 2). Table 2. Solar System Abundances of the Elements ... 

Phosphate rock is calcinedto remove carbonaceous material before being oigested with sulfuric acid. Several different fluidization... 

The veins are composed mostly of quartz and a small amount of sulfide minerals (pyrite, pyrrhotite, arsenopyrite, chalcopyrite, sphalerite, and galena), carbonate minerals (calcite, dolomite) and gold, and include breccias of the host rocks with carbonaceous matters. Layering by carbonaceous matters has been occasionally observed in the veins. Banding structure, wall rock alteration and an evidence of boiling of fluids that are commonly observed in epithermal veins have not been usually found. 

Increase of reservoir permeability and widening of the fissures and channels through the etching of carbonaceous rocks in limestone reservoirs by organic acids produced by anaerobic bacteria... 

The isotopic composition of carbon in carbonaceous organic material (kerogen) from ancient sedimentary rocks gives information on whether photosynthetic organisms were present during rock formation or not. It can also provide information on biological activities if cellular structures had already been destroyed. Sulphur can be used in a similar way (Schopf, 1999). 

Alien-King R, Grathwohl P, Ball W (2002) New modeling paradigms for the sorption of hydrophobic organic chemicals to heterogeneous carbonaceous matter in soils, sediments, and rocks. Adv Water Resour 25 985-1016... 

Carbonaceous chondrite A meteorite containing once-molten globules of rock called chondrules that are surrounded by carbon-containing species. 

Bulk rock analyses of carbonaceous chondrites exhibit a Cr excess from 1 to 2 s (Rotaru et al. 1992 Shukolyukov et al. 2003). The carbonaceous chondrites are not exactly solar in their Cr isotopic bulk composition, but taking into account that the components are more than 220 e apart, the match is very close and the idea that C chondrites are a fair representation of the solar system average is still reasonable. 

Feldspars are the most abundant minerals of igneous rocks, where their ubiquity and abundance of their components influence normative classifications. They are also abundant in gneisses, and may be observed in several facies of thermal and regional metamorphic regimes. Notwithstanding their alterability, they are ubiquitously present in sedimentary rocks, as authigenic and/or detritic phases. Only in carbonaceous sediments is their presence subordinate. 

Metalliferous sedimentary rock horizons occur as intercalated units between volcanic rocks of the 2.7 Ga Kidd-Munro assemblage (KMA) of the Abitibi subprovince, Canada (Hannington et al., 1999). The shale horizons are widely distributed within the KMA and commonly occur as carbonaceous (graphitic) and/or sulfidic argillaceous shale units. Multiple horizons may be present in any one drillcore, representing both primary depositional stratigraphy and subsequent fold repetition. 

This deposit is located in the north-east of Russia and belongs to a gold-arsenic type of low-sulphide formation (Abramson et al, 1980). It lies within a carbonaceous terrigenous rock of Triassic age and is associated with a dome-shaped uplift in a node of intersecting faults of various directions. The ore bodies consist of zones of silicification and kaolinization with veinlet-disseminated sulphide mineralisation. Gold is present in the form of finely-dispersed dissemination in arsenopyrite and pyrite. As an example. Figure 1 illustrates the distribution of Au and Mn in connection with commercial ore... 

Geological Setting The area is underlain by Birimian meta-volcanic and meta-sedimentary rocks that have been intruded by granites. The meta-volcanic rocks are of basaltic and gabbroic compositions and most have been altered to various schists. The metasedimentary rocks consist of sandstones, siltstones, tuffs, carbonaceous phyllites, tuffaceous phyllites, cherts and maganeferous rocks (Leube et al. 1990). 

Rutstein, M. S. (1979). Fibrous intergrowth of green muscovite and cross chlorite from shear zones of Pennsylvanian carbonaceous rocks in Rhode Island. Amer. Min. 64 151-155. 

The composition of fine particles varies from region to region, depending on the precursor emissions. In the northeastern USA, central Europe, and southeastern Asia, more than half of the composition is made up of sulphate particles, due to the combustion of high-sulphur coal and oil. The rest is made up of nitrate particles, carbonaceous material (elemental and organic carbon), and crustal matter (fugitive particles from soil, clay, and rock erosion). 

Some asteroids, thought to contain modest amounts of ices, might show cometary activity if they were to be perturbed into orbits that took them close to the Sun. Other asteroids originally accreted with ice components, which later melted. Such asteroids were then altered when fluids reacted with rock. Altered carbonaceous chondrites were discussed briefly in Chapter 6. Here we explore asteroid alteration in more detail. 

Major-element compositions (weight ratios of Mg/Si and Al/Si) for mantle rocks (peridotites) and estimates of the primitive mantle composition of the Earth compared with various groups of chondrites and the Sun. No mixture of chondrite types provides an exact match to the primitive mantle composition, although some carbonaceous chondrites provide the closest match. Modified from Righter et al. (2006). 

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