Solar System common minerals

The largest class of meteorite finds is stony meteorites, made principally of stone. The general stony classification is divided into three subclasses called chondrites, carbonaceous chondrites and achondrites, and it is at this level of distinction at which we will stop. Before looking at their mineral and isotopic structure in more detail, it is useful to hold the composition of the Earth s crust in mind here for comparison. The Earth s crust is 49 per cent oxygen, 26 per cent silicon, 7.5 per cent aluminium, 4.7 per cent iron, 3.4 per cent calcium, 2.6 per cent sodium, 2.4 per cent potassium and 1.9 per cent magnesium, which must have formed from the common origin of the solar system. 

Among the elements that make up rocks and minerals, silicon, magnesium, and iron are of almost equal abundance followed by sulfur, aluminum, calcium, sodium, nickel, and chromium. Two of the most common minerals in meteorites and in the terrestrial planets are olivine ((Mg,Fe)2Si04) and pyroxene ((Mg,Fe,Ca)Si03). The composition obtained by averaging these two minerals is very similar to the bulk solar system composition, so it is really no surprise that they are so abundant. 

Shortly after the condensation of the first minerals to form within the Solar System, thermal processing of refractory inclusions began. The overall processing of these materials into igneous rocks was short-lived, perhaps only 100000 years (Bizzarro et al. 2007). The critical constraints on the thermal histories of these objects is essentially limited to Type-B CAIs (Connolly Desch 2004), which have been generated by the experimental reproduction of these objects in the laboratory. Type-B CAIs are composed mostly of melilite, anorthite, aluminous spinel, and a titanium-rich pyroxene known in the parlance as fassaite (for a summary of minerals common to the Solar System see Appendix 1). The general consensus is... 

A1.2 Composition of common minerals in the Solar System The composition of common minerals in the Solar System is given in Table Al.l. 

In the solar system, carbon is thus the fourth most abundant element, almost as common as oxygen. There is however a very big difference between the abundance of these elements in the earth, the number of carbon atoms being only about two-thousandths of that of oxygen. When the earth was formed, carbon was present as volatile compounds, CH,, CO and CO2. Some of these stayed in the atmosphere, some were trapped in minerals, but to a great extent they escaped from the atmosphere due to the low gravitational force of the small planet earth. 

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