BORON-RICH MICAS AND CHLORITES FROM MIAROLITIC PEGMATITES

摘要

Rich in boron micas and chlorites are typical minerals in miarolic pegmatites rich in polychromic tourmaline. The detected for the first time and described herein micas are intermediate by their chemical composition between muscovite and boromuscovite. Peculiarities of their metric allow to suppose the possibility of the B setting in various structural positions: in tetrahedral one- at high boron content (boromuscovites) and/or octahedral one-at low B concentration (B-bearing muscovites). Thus, there could be revealed an isomorphic row: cookeite LiAl_4(AlSi_3)O_(10)(OH)_8-the hypothetical 《borocookeite》 LiAl_4(Bsi_3)O_(10)(OH)_8 within range of B_(IV)~(3+) 0.0-0.6 f.u. Isomorphism is realized in this row by two schemes: B_(IV)~(3+)->Al_(IV)~(3+) and 3Li_(VI)~+->Al_(VI)~(3+). B-bearing micas and chlorites were crystallizing in miarolitic cavities from rich-in-boron solutions at 390-240 deg C. They occur there as together (in the same pocket, so separately also. It is supposed that the forming of one or another mineral depended on alignment of K, Li, B and H_2O activities in solutions within noninteracted miarols.