Levantite, KCa3(Al2Si3)O11(PO4), a new latiumite group mineral from pyrometamorphic rock of the Hatrurim Basin, Negev Desert, Israel

Levantite, with the end-member formula KCa 3 (Al 2 Si 3 )O 11 (PO 4 ), is the phosphate analogue of latiumite, KCa 3 (Al 3 Si 2 )O 11 (SO 4 , CO 3 ) found in gehlenite–wollastonite hornfels on Har Parsa, Negev Desert, Israel. Levantite forms later zones on long-prismatic crystals of latiumite. Rarer homogeneous colourless levantite crystals up to 0.2 mm long and with mean composition (K 0.94 Ba 0.01 Na 0.01 □ 0.04 ) Σ1.00 (Ca 2.96 Mg 0.03 ) Σ2.99 {(Si 2.69 Al 2.06 Fe 3+ 0.16 P 0.06 ) Σ4.97 O 11 }[(PO 4 ) 0.65 (SO 4 ) 0.35 ] Σ1.00 were noted. Minerals of the levantite–latiumite series are associated with gehlenite, wollastonite, clinopyroxene of the esseneite–diopside series, anorthite and Ti-bearing andradite. Levantite crystalises in space group P 2 1 with unit-cell parameters a = 12.1006(9) A, b = 5.1103(4) A, c = 10.8252(9) A, β = 107.237(8)°, V = 639.34(9) A 3 and Z = 2. The structure of levantite is analogous to latiumite. It is formed by tetrahedral hybrid zweier double layers [(Si,Al) 10 O 22 ] connected by Ca atoms. Three Ca atoms linked to different double layers are bridged over by (PO 4 ) and minor (SO 4 ) groups. K atoms reside in the cavities between two superimposed zweier double layers. The measured micro-indentation hardness of levantite gave VHN 50 = 580(19) (mean of 14), range 550–611 kg/mm 2 , which correlates with 5 on the Mohs scale. Cleavage is good on (100). Twinning on (100) is polysynthetic or simple. The calculated density is 2.957 g cm –3 . Levantite is optically negative with α = 1.608(2), β = 1.618(2), γ = 1.622(2) (λ = 589 nm), 2V meas. = 70(5)° and 2V calc. = 64.3°. Dispersion of the optical axes r > v is weak; the optical orientation is: Z = b , X ^ c = 22–27°; and it is non-pleochroic. Minerals of the levantite–latiumite series from Israel show characteristic Raman spectra with the main bands at 994 cm –1 [ν 1 (SO 4 ) 2– ] and 945 cm –1 [ν 1 (PO 4 ) 3– ]. The band intensity ν 1 (PO 4 ) 3– /ν 1 (SO 4 ) ratio is well correlated with P and S contents in the investigated minerals. The strongest lines in the powder diffraction pattern [ d obs , A ( I , %) ( hkl )] are: 3.0762(100)(310), 2.8551(96)( $\bar 2$ 13), 2.9704(92)( $\bar 3$ 12), 2.8573(83)(013), 2.5552(66)(020), 2.8228(48)(212), 2.8893(40)(400), and 3.0634(30)(103).