Meteorites as Sources of Volatiles and Metals
If the resources of primary interest are volatiles, then, among meteorites, the carbonaceous chondrites are the target of choice. The concentrations of hydrogen, carbon, nitrogen, and sulfur in C1 chondrites are more than 100 times those in the lunar regolith: the C1s contain (by weight) 4 to 6 percent carbon, about 0.3 percent nitrogen, 6 percent sulfur, and 10 to 20 percent water (1 to 2 percent hydrogen). Most of the carbon, nitrogen, and sulfur is, like the hydrogen, compounded, though there may be some pure carbon.
If metals are the principal resource desired, then all classes of chondritic meteorites are of great interest. The abundance of free iron in a typical chondrite is much higher than on the lunar surface, where only meteoritic fragments can be found. And the amount of metallic nickel in a typical chondrite is about 100 times the nickel content of lunar regolith. As figure 11 shows, there is real variation in the Fetotal:Si atomic ratio [from about 0.4 in LL and some E chondrites (the EL subtype, including Indarch) to about 1.0 in C1 and some other E chondrites (the EH subtype, including Khairpur)], but the large majority of the chondrites landing on Earth (the Land H groups) have Fetotal:Si atomic ratios of 0.6-0.8. As shown in figure 11, the C3 chondrites and C2 chondrites contain fully as much total iron (relative to silicon) as the H chondrites; the amount of free metal in the chondrite, however, varies from about 1 percent in the C3s to about 20 percent in the H group,
Figure 12 shows the total concentrations of water and free metal in the major classes of chondrites.
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