Original paper
Kalifersite, a new alkaline silicate from Kola Peninsula (Russia) based on a palygorskite-sepiolite polysomatic series
Ferraris, Giovanni; Khomyakov, Alexander P.; Belluso, Elena; Soboleva, Svetlana V.
European Journal of Mineralogy Volume 10 Number 5 (1998), p. 865 - 874
30 references
published: Oct 5, 1998
manuscript accepted: Feb 26, 1998
manuscript received: Jul 29, 1997
Abstract
Abstract Kalifersite, (K, Na)5(Fe3+)7[Si20O50](OH)6·12H2O, is a new [001] fibrous silicate discovered in a drill core of a hydrothermally altered pegmatite in the urtite series at Mt. Kukisvumchorr (Kola Peninsula). The new mineral formed by crystallization from residual peralkaline liquids during the hydrothermal stage of the pegmatitic process. Pink-brownish; good {100} and {010} cleavages; D(meas) = 2.37(2) g/cm3. Biaxal (+); α = 1.523(2), ß = 1.525(2), γ= 1.550(2), 2V(meas) = 30(2)°, 2V(calc) = 32°; optically pseudo-orthorhombic, O.P (010); slightly pleochroic. SAED patterns show triclinic symmetry and streaks; a = 14.86(4), b = 20.54(4), c = 5.29(2) Å, α = 95.6(3), ß_= 92.3(3), γ = 94.4(3)° have been obtained from least-squares refinement of powder diffraction data; s.g. P1̄Z = 1. Comparison with sepiolite {Mg8[Si12O30](OH)4 • 12H2O; a = 13.40, b = 26.80, c = 5.28 Å, s.g. Pncn, Z =2} and palygorskite {Mg5[Si8O20](OH)2 • 8H2O; a = 13.27, b = 17.868, c = 5.279 A, ß = 107.38°, s.g. C2/ra, Z = 2} allowed to obtain for kalifersite a structural model which explains its characteristics. On the basis of P = [(Y2+)5-y'-z'(Y3+)y'□z'] [Si8O20](OH)2{(An+)(2z'-y')/n • m'H2O} (palygorskite module) and S = [(Y2+)8-y-z(Y3+)y□z] [Si12O30](OH)4{(An+)(2z-y)/n' ·mH2O} (sepiolite module), kalifersite is the P1S1 member (with y + y' = 7,z + z' = 6 and m + m' = 12) of a PpSs polysomatic series named palysepiole series. In kalifersite, the alkali cations A lie in octahedra which connect the F-octahedra belonging to the palygorskite/sepiolite framework. This feature and polysomatic aspects are discussed by comparison with biopyriboles, raite and, in general, 2: 1 layer silicates.
Keywords
kalifersite • new mineral • polysomatism • palygorskite • sepiolite • raite