Unlike the mineral distribution on Earth, no concentrations of specific minerals have thus far been found on the Moon. For example, while the carbon content of the Earth's crust is only twice that of the Moon's 200 ppm versus 100 ppm, large deposits of nearly pure carbon (coal) occur in many locations on Earth, while the Moon's carbon appears to be quite uniformly distributed over the entire lunar surface. The principal lunar-derived elements potentially required for the SPS, namely oxygen, silicon, aluminum and iron, all occur in lunar soil in quantities varying from 5% to 45% by weight, with oxygen and silicon being relatively uniform in distribution regardless of location. Aluminum is more prevalent in highlands soil and iron in mare regions. Other metallic elements found on the Moon, which may be useful as alloying agents in aluminum and iron alloys, or for various other applications, include calcium, magnesium, titanium, chromium, sodium, manganese and potassium. A third source of lunar materials is basin ejecta which consists of a combination of lunar rock and meteoric material. The lunar material is lunar soil which has been lithified by meteoric impact. This material is also referred to under the acronym KREEP, because it tends to be high in potassium (J<), Rare Earth Elements, and Phosphorus. The lunar surface and near subsurface are anhydrous and essentially devoid of carbon and organic material. They consist of rock, complex metal oxides and silicates. As described in the Handbook of Lunar Materials (reference #4), the principal lunar minerals consist of plagioclase feldspars, olivine and pyroxene. Significant amounts of ilmenite occur in mare regions, and small amounts of spinels and lesser amounts of many other minerals are widely distributed over the lunar surface. Table II lists the principal minerals in lunar materials.
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