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 A ◻ B (NaLi) C (Mg 3 Fe 2 3+ ) Si 8 O 22 (OH) 2 ] has a = 9.535(3), b = 17.876(6), c = 5.294(2) Å, β = 102.54°(1), V = 880.9 Å 3 , and unit formula A (K 0.07 Na 0.38 ) B (Na 0.70 Li 1.24 Ca 0.06 ) C (Mg 1.35 Fe 2+ 0.92 Mn 2+ 0.13 Zn 0.31 Fe 3+ 1.71 Al 0.10 Ti 0.06 Li 0.42 ) Si 8 O 22 (OH 1.51 F 0.47 ). Holotype ferriwhittakerite [ideally A Na B (NaLi) C (Mg 2 Fe 2 3+ Li) Si 8 O 22 (OH) 2 ] has a = 9.712(9), b = 17.851(23), c = 5.297(2) Å, β = 103.63°(5), V = 892.5 Å 3 , and unit formula A(K 0.13 Na 0.64 ) B (Na 1.27 Li 0.62 Ca 0.11 ) C (Mg 1.47 Fe 2+ 0.58 Mn 2+ 0.12 Zn 0.40 Fe 3+ 1.48 Al 0.10 Ti 0.12 Li 0.73 )Si 8 O 22 (OH 1.30 F 0.72 ). 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.)