BERYLLIUM 



89 



substitution of beryllium for silicon impairs the 

 stability of a crystal's structure. Hence, beryllium 

 is most concentrated in minerals whose structures 

 are most tolerant of the resulting distortion. Plagio- 

 clase feldspar probably contains much of the earth's 

 beryllium, but micas and clays are also important 

 hosts. 



During the crystallization of a magma, beryllium 

 becomes progressively more concentrated in the 

 fluid as crystallization proceeds. One result of this 

 is an increasing concentration of beryllium in suc- 

 cessively younger rocks in genetically related suites. 

 This enrichment reaches a point where beryllium 

 minerals can form only in the presence of complex- 

 ing agents, such as F- or COs"", that keep an un- 

 usually large proportion of the beryllium in the 

 residual liquids. In igneous rocks the beryllium con- 

 tent therefore increases along with silica and alkali 

 contents. The average content of beryllium in peri- 

 dotite is less than 0.25 ppm, that of basalt and gab- 

 bro is about 0.5 ppm, and that of rhyolite and gran- 

 ite is about 5 ppm. Detailed study of each of these 

 groups shows the relations to be complex. For ex- 

 ample, in silicic rocks the beryllium content passes 

 through a maximum as silica content increases. In 

 addition, the average beryllium content of plutonic 

 rocks is higher than that of volcanic rocks, perhaps 

 reflecting the loss of beryllium in vapors during 

 volcanism. 



The very coarse texture of pegmatites has made 

 them difficult to sample for beryllium content, al- 

 though the coarseness facilitates the determination 

 in the field of the contents of beryl and other eco- 

 nomic minerals. 



In a series of related pegmatites, the beryllium 

 content can increase in successively intruded rocks 

 to a maximum of about 180 ppm; it then remains 

 rather uniform. This is apparently the maximum 

 concentration that can be reached through mag- 

 matic processes in magmas of granitic composition. 

 Much higher beryllium contents may characterize 

 beryl-rich inner zones of pegmatite dikes, but aver- 

 aging these with the larger beryl-poor outer zones 

 shows that few, if any, bodies contain more than 

 200 ppm overall, which corresponds to about one- 

 half of 1 percent beryl. This is the maximum grade 

 that can be expected in large bodies of pegmatite. 

 Most pegmatites contain much less and may average 

 a few tons of parts per million of beryllium. 



Beryllium is very scarce in most hydrothermal 

 deposits, generally constituting 1 ppm or less. Ores 

 formed by replacement commonly contain about as 

 much beryllium as the rock that was replaced. For 

 example, most tactites in limestone contain less than 



1 ppm beryllium, and replacement veins in granite 

 or gneiss commonly contain a few parts per million. 

 Certain hydrothermal deposits are low in base and 

 precious metals but are rich in beryllium. They gen- 

 erally contain fluorite, magnetite or hematite, car- 

 bonate minerals, zinc minerals, and if fluoritic, one 

 or more metals that, like beryllium, form water- 

 soluble fluoride complexes, such as tin, tungsten, 

 bismuth, manganese, rare earths, titanium, or nio- 

 bium. These metals are largely in oxygen com- 

 pounds; sulfide minerals are rather uncommon. 



Beryllium is released from the rock-forming min- 

 erals as they weather, and is incorporated in clay 

 minerals. Thereafter, it remains in clayey soil or 

 is carried oflf in suspension in running water. Most 

 coarse sedimentary materials — pebbles, sand, and 

 derived rocks — have low beryllium contents, corre- 

 sponding to that of the quartz that is generally the 

 dominant component. Near beryllium deposits, 

 coarse sediments may contain detrital particles of 

 beryllium minerals, many of which are resistant to 

 weathering. Industrial beryl, and gem chrysoberyl, 

 phenakite, and euclase (AlBeSi04(0H) ) have been 

 mined from such extremely local concentrations. 

 Very little migration of beryllium takes place in 

 solution in normal waters because the beryllium re- 

 leased upon weathering is quickly adsorbed by min- 

 eral particles. High acid or carbonate- or halide- 

 rich water can cause small-scale migration of beryl- 

 lium, but not on an economically important scale. 



The beryllium contents of rocks change very little 

 with metamorphism. Thus, most micaceous meta- 

 morphic rocks contain a few parts per million of 

 beryllium, and quartzite and marble contain very 

 little. 



MINERALS 



The only beryllium mineral that has had much 

 economic importance is beryl, which has yielded 

 nearly all the beryllium used in industry. Bertrand- 

 ite, phenakite, helvite, chrysoberyl, and baryhte are 

 known to occur in moderately large deposits. The 

 other 39 known beryllium minerals have been found 

 in only small amounts. It is possible that some of 

 them will become important, as bertrandite and 

 barylite have. Twenty years ago bertrandite and 

 barylite were thought to be very rare, but now they 

 are known to form large bodies of present or po- 

 tential economic value. The common or important 

 minerals are shown in table 17. 



TYPES OF BERYLLIUM DEPOSITS 



Beryllium deposits can be divided into two broad 

 categories: (1) pegmatitic, and (2) nonpegmatitic 



