Metamorphism oxide

Most igneous and metamorphic rocks are composed predominantly of alurninosiHcate minerals, including feldspar such as albite (NaAlSi Og) or anorthite (CaAl2Si20g) and crystalline forms of siHca such as quartz (Si02). Various mixed metal-plus-siHcon oxides such as oHvine [(Mg,Fe)2(SiO ] and... 

The concept of metric tensor becomes central whenever distances and projections are considered, particularly when least-square criterion are used, a point that will be discussed in Chapter 5. Let us ask the frequently raised question of how to find an expression in terms of old coordinates (e.g., oxide proportions) for a projection made in the non-Euclidian space. This could be the case for finding oxide abundances of a basalt composition projected in the Yoder and Tilley tetrahedron, or the oxide abundance of a metamorphic rock composition projected into an ACF diagram assuming that quartz is present. 

Other meteorite classes like C2, CO and ordinary chondrites contain much smaller inclusions less than 1 mm (MacPherson et al. 1988) and require ion microprobe techniques to evaluate the isotopic compositions. On the least metamorphosed side. Cl have very few inclusions or oxide grains, but are the carrier of the greatest amounts of stellar nanodiamond and other carbides (Anders and Zirmer 1993). As will be shown for Cr anomalies in carbonaceous chondrites, the survival of the mineral carriers of the anomalies also depends on the metamorphic grade of the meteorites. Nevertheless, isotopic anomalies have also been formd in higher metamorphic grade from other classes, especially in the reduced enstatite chondrites. 

Iron oxides (hematite and magnetite) are common minerais found in magmatic and metamorphic rocks and can be major to accessory minerais in a range of minerai deposit types. The range in chemicai composition of the various deposit type environments iikeiy controis the chemicai composition of iron oxides in minerai deposits, such that this compositionai variety can be used to fingerprint minerai deposit types (Carew 2004 Gosseiin etal. 2006 Beaudoin Dupuis 2009). 

By convention, rocks are divided into three groups magmatic (volcanic or extrusive and plutonic or intrusive), metamorphic and sedimentary rocks. Iron ores being the source of iron as a metal, are also rocks and are common in all three groups. Most rocks contain iron oxide minerals of varying nature and abundance. This chapter collects information about their occurrence (Tab. 15.1), properties and formation. 

Frost, B.R. Lindsley, D.H. (1991) Occurrence of iron-titanium oxides in igneous rocks. In Lindsley, D.H. (ed.) Oxide minerals. Reviews in Mineralogy 25, Min. Soc. Am., 433-468 Frost, B.R. (1991) Stability of oxide minerals in metamorphic rocks. In Lindsley, D.H. (ed.) Oxide minerals. Reviews in Mineralogy 25, Min. Soc. Am., 469-488 Fryer, J.R. (1979) The chemical applications of transmission electron microscopy. Academic Press, London New York, 231 p. 

Metamorphic reactions in anhydrous chondrites mostly involved recrystallization, although a few mineral changes occurred. Of particular interest is an oxidation reaction... 

McSween, H. Y. and Labotka, T. C. (1993) Oxidation during metamorphism of the ordinary chondrites. Geochimica et Cosmochimica Acta, 57, 1105-1114. 

The aqueous fluids formed by melting of ices in asteroids reacted with minerals to produce a host of secondary phases. Laboratory studies provide information on the identities of these phases. They include hydrated minerals such as serpentines and clays, as well as a variety of carbonates, sulfates, oxides, sulfides, halides, and oxy-hydroxides, some of which are pictured in Figure 12.15. The alteration minerals in carbonaceous chondrites have been discussed extensively in the literature (Zolensky and McSween, 1988 Buseck and Hua, 1993 Brearley, 2004) and were most recently reviewed by Brearley (2006). In the case of Cl chondrites, the alteration is pervasive and almost no unaltered minerals remain. CM chondrites contain mixtures of heavily altered and partially altered materials. In CR2 and CV3oxb chondrites, matrix minerals have been moderately altered and chondrules show some effects of aqueous alteration. For other chondrite groups such as CO and LL3.0-3.1, the alteration is subtle and secondary minerals are uncommon. In some CV chondrites, a later thermal metamorphic overprint has dehydrated serpentine to form olivine. 

It is difficult to believe that oxygen per se was available during metamorphism. However, it is known that at 500°-600°C. steam can react with carbons to give a surface oxide and hydrogen water would be available from clay minerals and bed moisture in the Antarctic strata, and this reaction could well have occurred at the high pressures prevailing in the seams. On the other hand,... 

It seems therefore that stable radicals are formed during diagenesis (possibly by aerial oxidation as well as enzymatic action), but it may be questioned whether it is these radicals that survive metamorphism and are observed in bituminous coals. One of the main chemical consequences of metamorphism is that much of the combined oxygen in peats is eliminated, and one would expect that if the majority of the free radical centers in peats were localized on oxygen atoms, they would mostly be eliminated during metamorphism. 

---