Darrellhenryite, 

NaLiAl₂Al₆(BO₃)₃Si₆O₁₈(OH)₃O,

a new mineral from the tourmaline supergroup

Milan Novák¹, Andreas Ertl², Pavel Povondra³, Michaela Vašinová Galiová⁴, George R. Rossman⁵, Helmut Pristacz², Markus Prem², Gerald Giester², Petr Gadas¹ and Radek Škoda¹

¹Department of Geological Sciences, Masaryk University, Kotlářská 2, 611 37, Brno, Czech Republic

²Institut für Mineralogie und Kristallographie, Geozentrum, Universität Wien, Althanstrasse 14, A 1090 Wien, Austria

³Department of Geochemistry, Mineralogy and Natural Resources, Charles University, Albertov 6, 128 43 Praha 2, Czech Republic

⁴Department of Chemistry, Masaryk University, Kotlářská 2, 611 37 Brno, Czech Republic

⁵Division of Geological and Planetary Sciences, California Institute of Technology, Pasadena, CA 91125-2500, USA

 ABSTRACT

Darrellhenryite, a new member of the tourmaline supergroup (relates to the alkali-subgroup 4), is a new Li-bearing tourmaline species derived from closely related elbaite by the substitution ^YAl_0.5^WO₁ ^YLi_-0.5^W(OH)_-1. It occurs in complex (Li-bearing) petalite-subtype pegmatite with common lepidolite, Li-bearing tourmalines, and amblygonite from Nová Ves near Český Krumlov, southern Bohemia, Moldanubian Zone, Czech Republic. This zoned pegmatite dike, crosscuts a serpentinite body enclosed in leucocratic granulites. Darrellhenryite forms columnar crystals (sometimes in parallel arrangement), up to 3 cm long and up 2 cm thick, associated with albite (cleavelandite), minor quartz, K-feldspar, petalite, rare polylithionite and locally rare pollucite. The optical properties and the single-crystal structure study (R1 = 0.019) of darrellhenryite confirm trigonal symmetry, ω = 1.636(2), ε = 1.619(2), birefringence: 0.017, space group R3m, a = 15.809(2), c = 7.089(1) Å, V = 1534.4(4) ų_, and Z = 3. The chemical analysis, in combination with the crystal structure refinement, gives the formula ^X(Na_0.58Ca_0.01ÿ_0.41) ^Y(Li_1.05Al_1.95) ^ZAl₆ (BO₃)₃ ^T(Si₆O₁₈) ^V(OH)₃ ^W(O_0.66F_0.34), which can be simplified to an ideal formula of NaLiAl₂Al₆(BO₃)₃Si₆O₁₈(OH)₃O. The strongest lines of the powder pattern [d in Å (I, hkl)] are 4.180 (39, 211), 3.952 (54, 220), 3.431 (73, 012), 2.925 (100, 122), 2.555 (90, 051), 2.326 (42, 511), 2.029 (42, 223), 2.021 (42, 152), 1.901 (50, 342), 1.643 (49, 603). The density is D_meas = 3.03(3) g/cm³, D_calc = 3.038 g/cm³. Darrellhenryite is likely related to Li- and B-rich but F-moderate environments in complex pegmatites; no influence of higher activity of O on the darrellhenryite formation is implied from its mineral assemblage. The name is for Darrell J. Henry, Professor of Geology at the Louisiana State University, Baton Rouge, USA, an expert on the mineralogy, petrology, crystal chemistry and nomenclature of tourmaline-supergroup minerals.

A portion of the type darrellhenreyite. The pink color comes from its manganese content.