Hydrothermal Crystallization of Lithium Silicates. Synthesis of Spodumene
Crystallization in systems containing lithium, alumina, and silica has frequently been studied both from the point of view of producing individual crystals of lithium aluminosilicates (which include a number of compounds with low and even zero thermal-expansion coefficients) and also from that of studying the conditions underlying the genesis of natural lithium minerals. As a result of these investigations carried out in dry systems and also in the presence of water, almost all the natural lithium aluminosilicates have been synthesized, together with a number of artificial lithium compounds with no natural analogs. The only exception is α-spodumene, which has never been synthesized with an adequate degree of reproducibility. This would appear rather unexpected in view of the fact that spodumene, being a typical mineral of lithium-rich granite pegmatites, which are frequently formed in the final stages of the pegmatitic process, should not really require very high temperatures and pressures for its formation. Nevertheless, attempts at synthesizing α-spodumene up to 4000 atm and 600°C have usually proved unsuccessful [1–6]. Instead of α-spodumene, eucryptite, ß-spodumene, petalite, and a number of artificial lithium compounds have been obtained. In individual experiments of Roy and Osborn  at 375–500°C and 840 atm, a phase interpreted as α-spodumene was obtained. Under similar conditions (360–400°C) Barrer and White obtained α-spodumene . However, in both cases the products synthesized had lattice parameters differing from those of natural spodumene and higher refractive indices, indicating their contamination with impurities probably arising from the autoclave walls.
KeywordsLithium Chloride Individual Crystal Acicular Crystal Original Mixture LiCI Solution
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