Other| August 01, 1996 A new hyper-calcic amphibole with Ca at the A site; fluor-cannilloite from Pargas, Finland Frank C. Hawthorne; Frank C. Hawthorne CNR Centro di Studio per la Cristallochimica e la Cristallografia, Pavia, Italy Search for other works by this author on: GSW Google Scholar Roberta Oberti; Roberta Oberti Search for other works by this author on: GSW Google Scholar Luciano Ungaretti; Luciano Ungaretti Search for other works by this author on: GSW Google Scholar Joel D. Grice Joel D. Grice Search for other works by this author on: GSW Google Scholar American Mineralogist (1996) 81 (7-8): 995–1002. https://doi.org/10.2138/am-1996-7-821 Article history first online: 02 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Twitter LinkedIn Tools Icon Tools Get Permissions Search Site Citation Frank C. Hawthorne, Roberta Oberti, Luciano Ungaretti, Joel D. Grice; A new hyper-calcic amphibole with Ca at the A site; fluor-cannilloite from Pargas, Finland. American Mineralogist 1996;; 81 (7-8): 995–1002. doi: https://doi.org/10.2138/am-1996-7-821 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyAmerican Mineralogist Search Advanced Search Abstract Electron microprobe analysis of amphiboles from Pargas, Finland, shows up to 2.42 Ca apfu (atoms per formula unit), far in excess of the usual maximum value of 2.00 Ca apfu observed in amphiboles. The most Ca-rich composition is (K0.12Na0.35Ca0.52)(Ca1.92−Mn0.052+Fe0.032+)(Mg3.73Fe0.432+Ti0.02Al0.82)(Si5.63Al2.37)O22[(OH)0.46F1.54]. Fluor-cannilloite, ideally CaCa2(Mg4Al)(Si5Al3)O22F2, is a new amphibole species in which Ca is dominant at the A site. Fluor-cannilloite occurs as isolated anhedral grains and small granular aggregates in a marble together with calcite, muscovite, anorthite, aluminous diopside, pyrope, and fluorite. It is grayish green with a grayish white streak, brittle, H = 6, Dmeas = 3.05 g/cm3, and shows perfect {110} cleavage. In plane-polarized light, it is pale greenish gray to almost colorless, rather cloudy and mottled in appearance, and is not pleochroic. Fluor-cannilloite is biaxial positive, α = 1.611(2), β = 1.616(2), γ = 1.633(2), 2V = 49(2)°, dispersion weak r > v. It is monoclinic, space group C2/m, a = 9.826(4), b = 17.906(9), c = 5.301(3) Å, β = 105.41(4)°, V = 899.2 Å3, Z = 2. The ten strongest X-ray diffraction lines in the powder pattern [d in Å(I)(hkl)] are 8.936(4)(020), 8.355(3)(110), 3.366(4)(131), 3.107(7)(310), 2.686(10)(151), 2.578(10)(061), 2.328(4)(351), 2.165(6)(171), 2.036(5)(202), 1.435(9)(4.10.1).The structures of fluor-cannilloite and another Ca-rich amphibole from Madagascar were refined to R indices of ∼1.5% using reflection intensities collected with MoKα X radiation. Site populations were assigned from the refined site-scattering values, considerations of mean bond lengths, and the unit formulas calculated from the electron microprobe analyses. Both the electron microprobe data and the site-scattering refinements show significant Ca (up to 0.52 apfu) together with Na and K at the A site. Both A2 and Am sites are occupied, with the A2 site having the higher electron density. Local bond-valence considerations indicate that Ca is equally partitioned between the A2 and Am sites, whereas K occupies Am and Na occupies A2. This content is PDF only. Please click on the PDF icon to access. First Page Preview Close Modal You do not have access to this content, please speak to your institutional administrator if you feel you should have access.