Minerals chert

Mercury ore deposits occur in faulted and fractured rocks, such as limestone, calcareous shales, sandstones, serpentine, chert, andesite, basalt, and rhyolite. Deposits are mostiy epithermal in character, ie, minerals were deposited by rising warm solutions at comparatively shallow depths from 1—1000 m (6). 

Berg-kalk, m. rock time (Geol.) mountain limestone. -kiesel, m. rock flint, chert felsite. -kohle,/. (mineral) coal, -kork, m. mountain cork (a light form of asbestos), -kreide, /. rock lime, -kristall, -krystall, m. rock crystal (transparent quartz), -kupfer, n. native copper, -lasur, /. azurite. -leder, n. mountain leather (a form of asbestos), -maun, m miner. 

Heavy Rare Earth Element). Therefore, it is considered that negative Ce and positive Eu anomalies in hydrothermally altered volcanic rocks, Kuroko ores, and ferruginous chert and LREE enrichment in the Kuroko ores have been caused by hydrothermal alteration and precipitations of minerals from hydrothermal solution responsible for sulfides-sulfate (barite) mineralization. 

Positive Eu anomaly is observed for hydrothermal solution issuing from the hydrothermal vent on the seawater at East Pacific Rise (Bence, 1983 Michard et al., 1983 Michard and AlbarMe, 1986). Guichard et al. (1979) have shown that the continental hydrothermal barites have a positive Eu anomaly, indicating a relatively reduced environment. Graf (1977) has shown that massive sulfide deposits and associated rocks from the Bathurst-Newcastle district. New Brunswick have positive Eu anomalies. These data are compatible with positive Eu anomaly of altered basaltic rocks, ferruginous chert and Kuroko ores in Kuroko mine area having positive Eu anomaly and strongly support that Eu is present as divalent state in hydrothermal solution responsible for the hydrothermal alteration and Kuroko mineralization. 

Main opaque minerals are chalcopyrite, pyrite, pyrrhotite, sphalerite and bornite (Table 2.22). These minerals commonly occur in massive, banded and disseminated ores and are usually metamorphosed. Hematite occurs in red chert which is composed of fine grained hematite and aluminosilicates (chlorite, stilpnomelane, amphibole, quartz) and carbonates. The massive sulfide ore bodies are overlain by a thin layer of red ferruginous rock in the Okuki (Watanabe et al., 1970). Minor opaque minerals are cobalt minerals (cobaltite, cobalt pentlandite, cobalt mackinawite, carrollite), tetrahedrite-tennantite, native gold, native silver, chalcocite, acanthite, hessite, silver-rich electrum, cubanite, valleriite , and mawsonite or stannoidite (Table 2.22). 

The best sealed-in minerals are zircons, zirconium silicate minerals which are formed when melted lava on the flanks of volcanoes solidifies. When the zircons crystallize out, they incorporate radioactive uranium (in particular 238U), which decays in several steps, leading Anally to the lead isotope 208Pb. The rate of decay is very low, as the half-life of uranium-238 is 4.5 x 109 years. Thus, the U-Pb-zircon method for age determination of Precambrian rock is very important. The fossils studied by Schopf were sandwiched between two lava layers (Schopf, 1999). The volcanic layers were dated to 3.458 0.0019 x 109 years and 3.471 0.005 x 109 years the age of the fossil layer (Apex chert) was thus determined to be about 3.465xlO9 years. 

At the end of 2003, new research results led to sensational headlines Minerals Cooked Up in the Laboratory Call Ancient Microfossils Into Question was the title chosen by Richard A. Kerr for his article in Science dealing with synthetically prepared silicate carbonates. Their microstructures show morphologies which look exactly like those of filaments which had been assigned as cyanobacterial microfossils of the Precambrian Warrawoona chert formation in western Australia. The synthetic structures consist of silicate-encapsulated carbonate crystals, and in part have a helically twisted morphology reminiscent of biological objects. Simple... 

The pressure and temperature associated with long-term burial in the sediments eventually converts BSi into chert and quartz, both of which are crystalline. This conversion process involves the partial dissolution of BSi followed by its reprecipitation. Reprecipitation occurs within and upon BSi and probably on clay minerals... 

Ca (aq), Mg (aq), and HCOjCaq). Silicate weathering is an incongruent process. The most important of these reactions involves the weathering of the feldspar minerals, ortho-clase, albite, and anorthite. The dissolved products are K (aq), Na (aq), and Ca (aq), and the solid products are the clay minerals, illite, kaolinite, and montmorillonite. The weathering of kaolinite to gibbsite and the partial dissolution of quartz and chert also produces some DSi,... 

Si02 is one of the most abundant compounds in nature. It forms a number of minerals and several varieties whose names are quite familiar agate, car-nelian, sard, amethyst, chalcedony, flint, and chert. All are composed of Si02 with only small or trace amounts of other elements or compounds included during crystallization. In many cases it is the additional components that impart the peculiar color, optical, or physical properties to these minerals. The names are familiar because since ancient times these minerals were used or commonly set in jewelry. All of the names are varieties of the mineral quartz, the stable form of SiOj, formed at ordinary temperatures and pressures. Si02 also forms several polymorphs, which are mentioned below. 

The spectra of the green laser-induced luminescence represented in Fig. 4.4a, together with their decay time, also allows its association with These luminescence spectra strongly differ from the spectral parameters of all known uranyl minerals. For this reason it is not possible to connect this type of green luminescence with finely dissipated uranyl phases. On the other hand, this luminescence is very similar in such different host minerals as sedimentary apatites, opalites, chalcedony, chert, quartz and barites. Luminescence independence from the minerals structure evidences that it may be connected with uranyl adsorption on the minerals surface, supposedly in the form of (UO2 X nH20)2+. 

In weathering situations, saturation of fluids with SiC relative to any species of pure silica is probably only rarely achieved. In continental and shallow sea deposits, silica is precipitated in some initially amorphous form, opaline or chert when lithified or extracted by living organisms. Authigenically formed silicates are probably not in equilibrium with quartz when they are formed. As compaction increases in sediments, silica concentrations in solution are again above those of quartz saturation (15 ppm) and again it must be assumed that the diagenetic minerals formed are not in equilibrium with a silica polymorph except where amorphous silica is present. It is possible that burial depths of one or two kilometers are necessary to effectively stabilize that quartz form. It must be anticipated that the minerals formed under conditions of silica saturation near the earth s surface will be a minority of the examples found in natural rock systems. 

Sepiolite and palygorskite have a rather special composition and seem to be related to specific mineral parageneses. They appear to be stably associated with montmorillonite, corrensite, serpentine, chert, sulfates, carbonates and various salts. They are found in deposits typified by processes of chemical precipitation or solution-solid equilibria (Millot, 1964) and are therefore rarely associated in sediments with large quantities of detrital minerals. Their chemical environment of formation is in all evidence impoverished in alumina and divalent iron. Their frequent association with evaporites, carbonates and cherts indicate that they came from solutions with high chlorinity. 

The use of the "closed system" to describe the assemblages in these closed basins seems justified in that frequently, most always, in fact, the number of clay minerals present in the sediments discussed above is two or more. The omnipresence of amorphous silica or chert raises the total number of phases to three. In an essentially three-component system, Mg-Si-Al or possibly four if H+ is considered, this indicates that the chemical components of the minerals are present in relatively fixed quantities in the chemical system which produces the mineral assemblages. None of the first three components is "mobile", i.e., its activity is independent of its relative mass in the solids or crystals present. However, there are sediments which present a monophase assemblage where only one variable need be fixed. Under these conditions sepiolite can be precipitated from solution and pre-existing solid phases need not be involved. 

STABLE ISOTOPE PALEOALTIMETRY USING SILICATE PROXIES Cherts and clay minerals... 

In order to overcome these problems, interest was focussed on that portion of the organic matter trapped in mineral precipitates which formed synchronously with sedimentation. In these cases, the material is hermetically sealed in the crystalline matter and may survive with relatively little subsequent alteration. Such preservation is common in cherts which are chemical precipitates of silica and now comist of fine grained quartz. These rocks offer the best chance for successful preservation of truely Precambrian molecular fossils. Modem microprobes and spectrophotometer microscopes allow the non-destructive analysis of organic matter enclosed in mineral crystals. Laser bombardment of microscopic... 

Models for the formation of Precambrian sediments suggest that the chemical sediments (such as cherts) of the Isua supracrustal belt have formed as shallow water deposits. This is in agreement with structures locally preserved in the metacherts of the sequence. After deposition, the supracrustals were folded and metamorphosed. Finally, the metamorphism reached lower amphibolite facies and in consequence, most of the primary minerals became recrystallized. As a result all chert now appears as quartzite. But apparently metacherts, magnetite iron formation and quartz carbonate rocks have retained their major element chemistry largely unaltered during metamorphism (Nutman et al., 1984) 119). 

Flint is a common name applied to any material, rock or mineral, that is composed mostly of massive cryptocrystalline quartz. This word is usually used to describe dark-colored chert nodules found in limestones. The term flint is often used by anthropologists to describe homogeneous siliceous materials that have been used to make tools or weapons, regardless of their actual composition. 

Diamond (D50) described the types of silica that can take part in ASR. They include quartz if sufficiently strained or microcrystalline, tridymite, cristobalite and glass or other amorphous forms, which occur in varying combinations in opals, flints, cherts and other rock types. Opals are especially reactive. Macroscopic, unstrained crystals of quartz appear to be Linreactive but are possibly not completely inert. Some silicate minerals and volcanic glasses may undergo reactions similar to ASR. 

Oligocene to Miocene origin, as determined by microthermometry (Kretzschmar, 1982). The chert mineralization and the supply of iron was controlled by low-temperature hydrothermal fluids. In the immediate vicinity of the fungal stromatolites, haematitic veins are present and support the assumption of hydrothermal influence. 

The INAA data showed that 42.4% of the samples visually identified as chert in the field were rich in feldspar minerals (see Table II), and confirmed that the reference collection was made of quartzite, (K-feldspar-rich rock and Na-feldspar-rich rock), graywacke, and chert (8). 

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