FRANKAMENITE K_3Na_3Ca_5(Si_(12)O_(30))F_3(OH) centre dot H_2O - A NEW MINERAL, TRICLINIC VAREITY OF CANASITE FROM CHAROITITES

摘要

The mineral has been found in well known charoitic rocks of Murunsky massif (Sokha Yakutia). Unlike the monoclinic canasite from Khibiny, frankamenite has a triclinic unit cell, which is the minimum fragment of its crystal structure, and contains the only one silicate tube of Si_(12)O_(30) composition. Within charoitites it is present as prismatic crystals up to 10 mm in size. The choice of the unit cell depends on distribution of Ca and Na atoms in octahedral sites and is connected with higher fluorine content, in respect to canasite from Khibiny. All the necessary data on physical properties and crystallochemical composition of frankamenite are presented in the paper. The mineral has been named to the memory of a prominent crystallographer - professor V. A. Frank-Kamenetsky (1915-1994).