It also makes up much of the lunar highlands; the Genesis Rock, collected during the 1971 Apollo 15 mission, is made of anorthosite, a rock composed largely of anorthite. Anorthite was discovered in samples from comet Wild 2, and the mineral is an important constituent of Ca-Al-rich inclusions in rare varieties of chondritic meteorites.
Twins may be wider than the twins in albite,
but x-ray diffraction or other tests are
required to differentiate them for certain.after Perkins, 309Anorthite in Hand SampleAnorthite is the light mineral in this hand sample.
Scanning electron micrograph of anorthite
Since Luna lacks any known deposits of bauxite, the ore most commonly used on earth for aluminum production, anorthite (CaAl2Si2O8) is most commonly proposed as a lunar substitute.[1] Anorthite could be separated from the lunar highland material Anorthosite with mechanical methods. It could then be reduced through various chemical and electrochemical methods to produce aluminum.
The Anorthosite which makes up the Lunar highlands is a mix of Plagioclases, Olivines, and Pyroxenes. To separate the anorthite, anorthosite must be ground. Then, magnetic separation could leave the non-magnetic anorthite.
A Geologic Assessment of Potential Lunar OresDAVID S. McKAY and RICHARD J. WILLIAMSLarge amounts of silicon and aluminum and smaller amounts of other elements will be needed to construct large space structures such as solar power satellites. An analysis of transportation costs indicates that it may be much less expensive to use lunar material. Although bulk lunar soil is not a suitable feedstock for extracting metals, certain minerals such as anorthite and ilmenite can be separated and concentrated. These minerals can be considered as potential ores of aluminum, silicon, titanium, and iron. A separation and metal extraction plant could also extract large amounts of oxygen and perhaps hydrogen from these minerals. Anorthite containing 19 percent aluminum and 20 percent silicon can be concentrated from some highland soils where it is present in amounts up to 60 percent. Ilmenite containing 32 percent titanium and 3 7 percent iron can be concentrated from some mare soils where it is present in amounts up to 10 percent. The ideal mining site would be located at the boundary between a high-titanium mare and a high-aluminum highlands. Such areas may exist around the rims of some eastern mania, particularly Tranquilitatis. A location on Earth with raw materials as described above would be considered an economically valuable ore deposit if conventional terrestrial resources were not available.INTRODUCTIONG. K. O'Neill (ref. 1) points out the potential economic advantage of using nonterrestrial resources, particularly lunar resources, in constructing large space structures in Earth orbit. This advantage accrues because the gravitational well of the Moon is only about 1/22 that of Earth For the very large mass of material necessary to build a large space structure such as a solar power station, this difference in gravitational energy represents a significant savings in launch costs between the Earth and the Moon.The construction of a large solar power station will require thousands of tons of aluminum and silicon. In addition, a large mass of shielding is necessary to protect the construction crew from exposure to cosmic rays and solar flares. How much of this material can be derived from the Moon? Do economically useful materials exist on the Moon? Can these materials be concentrated and processed to produce the material necessary for constructing large space structures? In the following sections, these questions are considered in the context of the extensive lunar data base resulting from the Apollo program.BULK LUNAR SOIL AS A RESOURCEBulk lunar soil, (The term "soil" is used here to describe the fine-grained debris layer which overlies much of the surface of the Moon; the term "regolith" is also often used for this layer), contains as major constituents aluminum, silicon, iron, titanium, magnesium, calcium, and oxygen. It has been previously proposed that lunar soil could be used directly as an industrial feedstock from which all of these constituents could be extracted in a single plant using a variety of processes (ref. 2) However, nearly all commercial metal-extraction plants are designed to process a single feedstock containing a small number of elements and to extract a single metal or, at most, two or three metals. The plants can then be optimized by a single process designed specifically for the feedstock and the end-product metal. For maximum extraction efficiency, the feedstock is usually concentrated by beneficiation processes before it enters the extraction plant. A plant designed to extract six or seven elements from bulk lunar soil would be extremely complex, it could not be optimized for a single element, and it would have to overcome such complex problems as cross reactions and blocking reactions.Extensive experience has shown that it is nearly always far cheaper to concentrate an ore by beneficiation technique than to use the unconcentrated ore directly in the energy-intensive chemical processing plant. For example, energy used to concentrate iron ore is only about 1/10 that used in smelting and refining per ton of processed iron (ref. 3) Without concentration, the smelting and refining costs would be much greater and the processes themselves would need to be redesigned.Based on these considerations and drawing on the extensive experience of commercial metal extraction, we suggest that it is more practical to limit the extraction effort to a small number of elements and to concentrate lunar materials that contain only those elements. The metal-extraction plants can then be designed specifically for those elements using the least complicated processes availableIn following this philosophy, we have chosen aluminum as the primary metal to be extracted from lunar material - the mineral anorthite is the primary aluminum resource. In companion papers (refs. 4, 5), the mining and ore concentration operations are discussed as well as the chemical processing necessary to extract aluminum from anorthite. Silicon and oxygen are valuable by-products of this extraction process. Because aluminum and silicon may not be suitable for some applications (e.g., where high structural strength is required), we will also extract, on a smaller scale, iron and titanium from the mineral ilmenite. Again, references. 4, 5, discuss the procedures for mining and concentrating the ilmenite and for chemically extracting its metals and oxygen. A by-product of ilmenite concentration may be recovery of solar-wind hydrogen which can then be used for propulsion fuel or for life-support needs when combined with oxygen.ANORTHITE AS AN ALUMINUM RESOURCEAluminum may be used extensively to construct a large solar power station. Fortunately, the Moon contains abundant aluminum as an essential constituent of the mineral anorthite, the aluminum-rich end member of the plagioclase series. Pure anorthite - CaAl2 Si2O8 - contains (by weight) 19.4 percent aluminum metal, 20.2 percent silicon metal, 14.4 percent calcium metal, and 46.0 percent oxygen. Anorthite can be considered to be a potential aluminum ore in the sense that it is a naturally occurring concentration of aluminum from which it may be economically feasible to extract the metal. Bauxite, which contains about 25 percent aluminum, is currently the major terrestrial aluminum ore. However, terrestrial anorthite has been used in some countries as a commercial aluminum ore (ref. 6) The United States Bureau of Mines (ref. 7) recently studied the economics of extracting aluminum from anorthite using a lime-soda sinter process. They concluded that the cost of extracting aluminum from anorthite was within a factor of 2 of the cost of extracting aluminum from bauxite and would become even more competitive as the cost of bauxite increased. The Bureau of Mines is currently planning to build a pilot plant to extract aluminum from anorthite (ref. 8). Alcoa Corp., which recently purchased a large area of land in Wyoming estimated to contain as much as 30 billion tons of recoverable anorthosite (ref. 9), is developing plans to recover aluminum from this source.If anorthite is becoming attractive as a terrestrial aluminum resource, it is even more attractive as a lunar aluminum resource. The lunar crust contains a much higher proportion of anorthite than does the Earth's crust and the lunar highlands are particularly rich in anorthite.Table 1 presents Al2O3 data on lunar soils sampled by the Apollo and Luna missions (refs. 10- 12). Normative anorthite is calculated using a value of 36.6 percent Al2 O3 for pure anorthite and assuming that all the Al3O3 in a regolith will go into anorthite. Normative anorthite is a good measure of the theoretical maximum amount of anorthite that can be present. The true or modal anorthite content will always be somewhat less because some aluminum will be present in solution in pyroxenes and glasses. Table 1 shows clearly that the highlands contain notably more normative anorthite than the mare regions. It is also apparent that the highlands show considerable variation in normative anorthite content from site to site and that the Apollo 16 site is the region richest in anorthite.
A smelter is used to split the ore to produce pure aluminum metal, and optionally calcium metal, free oxygen, "silica" glass (SiO2), and perhaps pure silicon. Alternatively, anorthite could be processed to produce ceramics like "calcia" (CaO, aka "lime") and "alumina" (Al2O3) instead of the metals, or silica glasses with various properties depending upon the metal oxides existing in the final glass product and any other impurities added.
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