LOW-TEMPERATURE HEAT CAPACITY AND THERMODYNAMIC PROPERTIES OF NATURAL POLYLITHIONITE

Abstract

Polylithionite is a trioctahedral lithium mica with the general formula XY3Z4O10(F, OH)2. The sum of cations in the interlayer X positions is close to one. In addition to potassium, sodium and rubidium always occur as interlayer cations. The octahedral positions (Y) of natural polylithionite are mainly occupied by lithium and aluminum. Divalent cations (Fe, Mg, and Mn) are present in significant amounts only in iron-rich polylithionite varieties. Tetrahedral cations (Z positions) are mainly represented by silicon and minor aluminum (usually in a proportion of approximately 3.8 : 0.2), which allows polylithionite classification as a silica-rich mica. Among lithium micas, polylithionite shows the highest Li2O content of 5.5–8.0%, which corresponds to 1.5–2.0 formula units. Another characteristic feature of polylithionite composition is higher fluorine content compared with other lithium micas. Polylithionite is a typomorphic mineral of peralkaline pegmatites and rare-metal metasomatic rocks and is common in alkaline metasomatic zones. Together with other lithium micas, polylithionite can be used as a lithium ore and for the manufacturing of modern glass-ceramic materials.