Structural and chemical investigation of a zoned synthetic Cu-rich tourmaline

Author(s)

Andreas Ertl, Oleg S. Vereshchagin, Gerald Giester, Ekkehart Tillmanns, Hans-Peter Meyer, Thomas Ludwig, Ira V. Rozhdestvenskaya, Olga V. Frank-Kamenetskaya

Abstract

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 zone (which crystallized directly on the seed crystal) has the formula ∼

^X (Na

_0.8

_0.2)

^Y (Al

_2.0Cu

_0.9

_0.1)

^ZAl

₆

^T (Si

_5.1Al

_0.9)O

₁₈ (BO

₃)

₃

^V (OH)

₃

^W [O

_0.7F

_0.2 (OH)

_0.1] with lattice parameters a 15.835(1), c 7.093(1) A (R = 2.4%). The second zone has the formula ∼

^X (Na

_0.8

_0.2)

^Y (Al

_1.8Cu

_1.1

_0.1)

^ZAl

₆

^T (Si

_5.1Al

_0.7B

_0.2)O

₁₈ (BO

₃)

₃

^V (OH)

₃

^W [(OH)

_0.4F

_0.3O

_0.3] with a 15.824(1), c 7.087(1) A (R = 2.3%). The third zone (highest Cu content with ∼14 wt.% CuO) has the formula

^X (Na

_0.81

_0.19)

^Y (Cu

_1.72Al

_1.21

_0.07)

^Z (Al

_5.96Cu

_0.04) (BO

₃)

₃

^T (Si

_5.17Al

_0.48B

_0.35)O

₁₈

^V (OH)

₃

^W [(OH)

_0.63F

_0.37] with a 15.849(1), c 7.087(1) A (R = 2.5%). While

^[4]Al decreases from zone 1 to zone 3,

^[4]B increases (by chemistry and SREF), which could be explained by a decreasing temperature during tourmaline crystallization. Such a T-site occupancy is in agreement with the <T-O> distance, which strictly monotonically decreases from 1.625(1) to 1.616(1) A. We suggest that very small amounts of Cu are present at the Z site of all investigated tourmaline samples, but only in the Cu-richest zone (∼14 wt.% CuO) is the refined value for Cu at the Z site (∼1% of the total Cu) higher than the 3σ error. The YO

₆ octahedron of this Cu-richest known tourmaline is mainly occupied by Cu. Two of the six (Cu,Al)-O distances are significantly enlarged: Y-O1 with 2.031(2) A and Y-O3 with 2.170(2) A, while the other distances Y-O2 and Y-O6 with ∼1.951(2) A are significantly smaller. The proportion of the average of the two enlarged distances to the average of the other distances in the Cu-richest zone gives a value of ∼1.08, which is the highest value known so far for Cu-bearing tourmalines. We conclude that for the Cu-richest zone the Jahn-Teller effect appears to be verified.

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

Naturhistorisches Museum Wien (NHM), Saint Petersburg State University, Scientific Software Center

Journal

The Canadian Mineralogist

Volume

53

Pages

209-220

No. of pages

12

ISSN

0008-4476

DOI

https://doi.org/10.3749/canmin.1400078

Publication date

10-2015

Peer reviewed

Yes

Austrian Fields of Science 2012

105116 Mineralogy, 105113 Crystallography, 104024 X-ray structural analysis

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology

Portal url

https://ucris.univie.ac.at/portal/en/publications/structural-and-chemical-investigation-of-a-zoned-synthetic-curich-tourmaline(01cf8994-1627-469f-a2f5-cb08047b29c7).html