STRUCTURAL AND CHEMICAL INVESTIGATION OF A ZONED SYNTHETIC Cu-RICH TOURMALINE

摘要: A synthetic Cu-rich tourmaline crystal (Lebedev et al. 1988) consists of three different zones. Each zone was characterized by EMPA, SIMS, and single-crystal structure refinement (SREF). The first (which crystallized directly on the seed crystal) has formula ~ X (Na 0.8 □ 0.2 ) Y (Al 2.0 Cu 0.9 0.1 Z Al 6 T (Si 5.1 )O 18 (BO 3 V (OH) W [O 0.7 F ] with lattice parameters a 15.835(1), c 7.093(1) ( R = 2.4%). second 1.8 1.1 B [(OH) 0.4 0.3 O 15.824(1), 7.087(1) 2.3%). third (highest content ~14 wt.% CuO) 0.81 0.19 (Cu 1.72 1.21 0.07 5.96 0.04 5.17 0.48 0.35 0.63 0.37 15.849(1), 2.5%). While [4] decreases from 1 to 3, increases (by chemistry SREF), which could be explained decreasing temperature during crystallization. Such -site occupancy is in agreement –O> distance, strictly monotonically 1.625(1) 1.616(1) A. We suggest that very small amounts are present at site all investigated samples, but only Cu-richest (~14 refined value for (~1% total Cu) higher than 3σ error. octahedron this known mainly occupied Cu. Two six (Cu,Al)–O distances significantly enlarged: –O1 2.031(2) –O3 2.170(2) A, while other –O2 –O6 ~1.951(2) smaller. proportion average two enlarged gives ~1.08, highest so far Cu-bearing tourmalines. conclude Jahn-Teller effect appears verified.