366 



UNITED STATES MINERAL RESOURCES 



or mining for lithium minerals. Rubidium is not 

 known to form any minerals of its own and occurs 

 only as a minor constituent in minerals of other 

 kinds, especially potassium minerals, and thus ap- 

 pears destined to continue as a byproduct. Francium, 

 atomic number 87, is virtually nonexistent and may 

 be disregarded in any discussion of mineral re- 

 sources. 



The phrase "rare alkalis" is to some degree mis- 

 leading. The known quantities of lithium and cesium, 

 and probably also rubidium, obtainable under eco- 

 nomic conditions resembling those of the present or 

 the recent past are far greater than the amounts 

 needed for current use or even for any but the most 

 fanciful uses predicted for coming decades. New dis- 

 coveries have often made supplies available to the 

 market long before a demand for the supplies ma- 

 terialized. Publicity about these discoveries, which 

 too frequently magnifies evidence that uses of these 

 commodities will increase, tends to put the merit of 

 even good deposits in question when after some years 

 they have still not been mined, for the fact that the 

 shortcoming lies not in the supply but in the de- 

 mand may go unrecognized. The adequacy of lithium 

 reserves to support new uses has been questioned 

 even in recent years. Yet it was known two decades 

 ago, and has been stated in the published record 

 since at least 1955, that lithium reserves are enor- 

 mous and that large additional reserves could almost 

 certainly be discovered, as in fact they have been 

 in the intervening years. 



The geologic distribution of lithium, cesium, and 

 rubidium is in many respects parallel to the distri- 

 bution of the common alkali metals sodium and po- 

 tassium, which is expectable from their chemical 

 similarities. All the principal lithium minerals, as 

 well as the cesium mineral iwUucite, are obtained 

 from granitic pegmatite, which is a generally coarse- 

 grained rock consisting chiefly of sodic and potassic 

 feldspars, quartz, and muscovite. Most of the ru- 

 bidium and some cesium used commercially have 

 been extracted from residues of the processing of 

 lepidolite, a lithium-rich mica of pegmatite. Lithium 

 from brines, which have long been a modest source, 

 has in recent years come to dominate the market. 



Crustal-abundance estimates in table 71 show 



Table 71. — Crustal abundance, in parte per million, of rare 

 alkali metals 



[Data from Heier and BiUings (1970)] 



rubidium as the most common of the rare alkalis, 

 lithium as a distant second, and cesium as very 

 meager. The abundance of rubidium may surprise 

 those whose chief acquaintance with rare alkalis is 

 through knowledge of industry patterns or aware- 

 ness of the absence of deposits comparable to those 

 of lithium and cesium. Rubidium seems to substitute 

 so readily for potassium in minerals that it is never 

 greatly concentrated in nature, whereas lithium and 

 cesium are less able to proxy for other elements and 

 thus must under some conditions form independent 

 minerals. Granitic rocks are the predominant host 

 of all the rare alkalis. During weathering and sedi- 

 mentation, rubidium and lithium, and probably 

 cesium as well, are for the most part dispersed in 

 clays. All deposits that have been economic sources 

 of rare alkalis formed either in the pegmatite phase 

 of granitic activity or through the development of 

 unusual varieties of brine. 



LITHIUM 



Lithium is by far the most economically important 

 of the rare alkalis, and for this reason it will be 

 discussed first and at greatest length. 



Most users of lithium products purchase lithium 

 in the form of manufactured chemical compounds, 

 of which the most common are the carbonate, hy- 

 droxide, bromide, chloride, hypochlorite, and stear- 

 ate, and butyl lithium. Lithium metal and alloys are 

 also produced. Lepidolite and petaJite and lesser 

 quantities of other lithium minerals go directly into 

 some kinds of glass and ceramics. Additional uses 

 of lithium products are in grease, in the manufac- 

 turing of air-conditioning systems and alkaline stor- 

 age batteries, in fluxes for welding and brazing, and 

 in metallurgy. 



Two of the more frequently mentioned potential 

 uses for lithium could someday cause a very great 

 increase in demand. One is for anodes and as a 

 constituent of the electrolyte in storage batteries to 

 power electric automobiles. The other is as an 

 energy source, to breed tritium for fusion reactions. 



The United States is generally self suflficient in 

 lithium and will remain so under any likely future 

 circumstances. The only shortage is in lepidolite and 

 petalite for glass and ceramics, and substitution may 

 be practicable for some of these uses. Unfortunately, 

 domestic production figures have not been published 

 for many years, and few export figures are avail- 

 able; thus, it is impossible to calculate relationships 

 among production, consumption, imports, and ex- 

 ports. 



Lithium was obtained chiefly from pegmatites 

 throughout most of the history of the industry, 



