Meteorites, general information

Based on information from these sources, scientists estimate that the nucleus of a comet consists of about 42 percent volatile compounds (about 80 percent of which is water) and 58 percent solid particles, generally described as "dust." About 45 percent of this nuclear dust is similar in chemical composition to the carbonaceous chondrites found in meteorites that is, they are primarily silicate in composition. (Carbonaceous chondrites are discussed at greater length in the next section.) Another 40 percent of the nuclear dust is organic in nature, that is, composed of carbon compounds of varying degrees of complexity. The final 15 percent of nuclear dust is composed of very small particles with masses of only a few atto-grams (10 l8g). 

Whether the ionization is positive or negative, TIMS requires careful sample preparation, often involving considerable chemical processing to separate and purify the element of interest. TIMS finds applications in geoscience, environmental analysis, cosmochemistry, biosciences, medicine, material science, and physics. Samples generally include soil, minerals, meteorites, and biological tissue. More information on the specifics of the TIMS technique and its applications is in the monograph by De Laeter (2001). 

FeCs, also known as cohenite, particularly when found mixed with nickel and cobalt carbides in meteorites (Hutchison 2007), was first identified by Ernst Wein-schenk, a German pioneer of microscopy and petrography in Munich. A general formula of cohenite is (FeNiCo)3C suggesting that this mineral also comprises the earth s core. In molten iron (above 1100°C) carbon can be dissolved up to 4.3%, about double the carbon content in cohenite (2.2%). The carbon solubility increases with temperature and when the solution slowly cools down, carbon in excess of 4.3 % separates as graphite. We have no information on carbon in the earth s core but we can speculate on it and assume that some was also mixed within other upper layers. A carbon content of 1.4-2.3 % has been found in native iron (Clarke 1920). 

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