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The crystal structure of phosphoellenbergerite, Mg12(Mg, Fe, □)2(PO4, PO3OH, AsO4)6(PO3OH, CO3)2(OH)6,P63mc,a =12.467(2) A,c = 5.0437(4) A, Z=1, has been refined to R = 0.027 for 1009 reflections. PO3OH groups on 3-fold axes are partially replaced by CO3 groups, as is the case for the structurally related holtedahlite. The distribution of protons among three structural sites is discussed. Electron microprobe analysis, X-ray powder diffraction pattern, and physical and optical properties are given.

Kristiansenite occurs as a late hydrothermal mineral in vugs in an amazonite pegmatite at Heftetjern, Tordal, Telemark, Norway. Tapering crystals, rarely up to 2 mm long, are colourless, white, or slightly yellowish. The mineral has the ideal composition Ca2ScSn(Si2O7)(Si2O6OH) and is triclinic C1 with cell parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) A, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, V = 1062.7(3) A3 (Z = 4). It has a monoclinic cell within ∼ 0.1 A and is polysynthetically twinned on {010} by metric merohedry. The strongest reflections in the X-ray powder pattern are [d in A, (I obs), (hkl)]: 5.18 (53) (1–11), 3.146 (100) (004), 3.089 (63) (−222), 2.901 (19) (221), 2.595 (34) (222), 2.142 (17) (−3–31). The Mohs’ hardness is 5½–6; Dcalc. = 3.64 g/cm3; only a mean refractive index of 1.74 could be measured. Scandium enrichment in the Heftetjern pegmatite and the crystal chemistry of scandium are briefly discussed.

The structure of the new disilicate kristiansenite, Ca2ScSn(Si2O7)(Si2O6OH), has been solved and refined from a crystal polysynthetically twinned by metric merohedry. The Bravais lattice is mC, with parameters a = 10.028(1), b = 8.408(1), c = 13.339(2) Å, α = 90.01(1), β = 109.10(1), γ = 90.00(1)°, but the space-group type is C1 (Z = 4). The twin law is m´, and the two components of the twin have nearly identical volumes: as a consequence, the Laue group of the twin is practically 2/m. By taking into account the twinning, an anisotropic refinement of the structure in C1 converged to R1 = 0.0242 for 259 refined parameters and 4862 observed reflections. The effects of the twinning by metric merohedry and of the volume ratio of the components on the symmetry of the diffraction pattern are discussed. The triclinic structure approximates within about 0.1 Å the monoclinic symmetry, the lower symmetry resulting mainly from cation ordering. Kristiansenite represents a new type of silicate structure and the first known case with the presence of protonated and normal disilicate groups at the same time. The disilicate groups and the other polyhedra centred on cations lie on different alternating (101) planes.

The crystal structure of synthetic holtedahlite, Mg12(PO3OH, PO4)(PO4)5(OH,O)6,P31m,a = 11.186(3),c = 4.977(1) A,Z = 1, has been refined toR = 0.033 for 718 observed reflections. Natural holtedahlite, Mg12(PO3OH, CO3)(PO4)5(OH, O)6,a = 11.203(3),c = 4.977(1) A, was refined toR = 0.031 for 1202 observed reflections. The structure contains pairs of face-sharing Mg-octahedra linked by edge-sharing to form double chains alongc. Hydrogen phosphate groups on three-fold axes are partially replaced by carbonate groups in natural holtedahlite. Structural similarities with ellenbergerite are pointed out.

KTENASITEwas originallydescribedby Kokkoros (1950)from the Kamariza mine, Laurium, Greece, where it occurs sparingly as blue-green, platy crystals up to I mm, in association with smithsonite, glaucocerinite, and serpierite. The symmetry of ktenasite, determined by Weissenberg studies, is monoclinic, space group P21/C.Kokkoros concluded from a partial microchemical analysis on 2'5 mg (Table II) that the mineral is a sulphate of copper and zinc with the formula (Cu,Zn)3S0iOH)4.2H20; there was, however, poor agreement between the observed and calculated densities. No other well-established occurrence of ktenasite seems to be reported in the literature. Ktenasite is mentioned by Rankin (1969) from the Ecton mine, Montgomery County, Pennsylvania, but no data are given and there must be doubt as to the identification. In 1972a green, platy mineral was detected by amateur collectors on material from the Glomsrudkollen zinc mine, Modum, Norway. It was subsequently identified as ktenasite by Raade, who also noted that Kokkoros's X-ray powder data were obtained on impure material. Some of the Norwegian ktenasite was later sent to Dr. A. Livingstone, Edinburgh, who, because of poor agreement with the published X-ray powder data, asked the British Museum (N.H.) for assistance. A description of this mineral is the subject of the present paper. Specimens are deposited in the British Museum (N.H.), London, the Mineralogical-Geological Museum, University of Oslo, and in the Royal Scottish Museum, Edinburgh. Occurrence. Glomsrudkollen mine is a contact deposit between quartz porphyry and limestone, situated within the Oslo Region (Goldschmidt, 1911). The dump at the entrance of the lowest adit, now partly removed, was locally rich in sulphides, mainly sphalerite, pyrite, and chalcopyrite. Rock and mineral fragments of the dump were commonly cemented to a sort of breccia by secondary sulphates, mainly gypsum. In some places ktenasite occurred rather abundantly as aggregates of thin platy crystals or laths up to I mm, often growing on, and thus younger than, clear gypsum crystals. A thin coating of a pale blue mineral, shown by microchemical tests to be a Cu-Zn-Al sulphate, has so far not been identified. Its X-ray powder pattern has broad and diffuse lines; scanning electron micrographs reveal an aggregate of platy crystals. The ktenasite-bearing material appeared when the dumps were taken out for road filling. Temporarily, large amounts of bianchite were seen to have precipitated as a white powder