Ferri-ottoliniite and ferriwhittakerite, two new end-members of the new Group 5 for monoclinic amphiboles

Mineralogical and crystal-chemical descriptions are provided for two end-members of the new Group 5 introduced by Leake et al. (2004) in the nomenclature of amphiboles. This new classification scheme recognizes the occurrence of compositions with B-site populations intermediate between (Ca,Na) amphiboles and (Mg,Fe,Mn,Li) amphiboles. Its implications for the classification and nomenclature of Li-rich amphiboles are also discussed in this paper. Holotype ferri-ottoliniite [ideally ArectangleB(NaLi) (C)(Mg3Fe23+) Si8O22 (OH)(2)] has a = 9.535(3) b = 17.876(6), c = 5.294(2)Angstrom, beta = 102.54degrees(1), V = 880.9 Angstrom(3), and unit formula (A)(K0.07Na0.38)(B)(Na0.70Li1.24Ca0.06)(C)(Mg1.35Fe0.922+Mn0.132+Zn0.31Fe1.713+Al0.10Ti0.06Li0.42) Si-8 O-22(OH1.51F0.47). Holotype ferriwhittakerite [ideally(A)Na(B)(NaLi) (C)(Mg2Fe23+Li) Si-8 O-22(OH)(2)] has a = 9.712(9), b = 17.851(23), c = 5.297(2) Angstrom, 103.63degrees(5). V = 892.5 Angstrom(3), and unit formula (A)(K0.13Na0.64) (B)(Na1.27Li0.62Ca0.11) (C)(Mg1.47Fe0.582+Mn0.122+Zn0.4Fe1.483+Al0.10Ti0.12Li0.73) Si8O22 (OH1..30F0.72). The root names have been chosen to acknowledge the contribution given to crystal-chemical studies of minerals, and particularly of amphiboles, by L. Ottolini (Pavia, Italy) and E.J.W. Whittaker (Oxford, U.K.).