ALBERT

Description: Fontarnauite was discovered in cores recovered from the Kütahya-Emet 2 and 188 (named here as Doğanlar) boreholes drilled in the Emet borate basin near the village of Doğanlar, Kütahya Province, Western Anatolia, Turkey. The Emet (or Emet-Hisarcık) basin is one of the Neogene basins in western Turkey bearing a borate-rich unit intercalated with Miocene sediments. Fontarnauite is most commonly associated with probertite, glauberite, and celestine and occurs as isolated colorless to light-brown prismatic crystals or as clusters of crystals less than 5 mm long. Fontarnauite is brittle, with a Mohs hardness of 21/2–3, and perfect {010} cleavage. D calc = 2.533 g/cm 3 . The new mineral is optically biaxial (–), α 1.517(2), β 1.539(2), 1.543(2) (590 nm); 2 V meas = 46(1)°; 2 V calc = 46°; X ^ a 95.0° (β obtuse); Y // b , Z ^ c 81.9° (β acute). Dispersion is r 〉 v , medium to weak. The chemical composition (electron microprobe; B and H from the crystal-structure refinement) is as follows: SO 3 17.75, B 2 O 3 38.66, CaO 2.26, SrO 18.98, Na 2 O 12.65, K 2 O 1.70, H 2 O 10.01, total 102.01 wt.%. The empirical formula (based on 15 O atoms per formula unit) is (Na 1.84 K 0.16 ) 2.00 (Sr 0.82 Ca 0.18 ) 1.00 S 1.00 B 5 H 5 O 15 ; the endmember formula is Na 2 Sr(SO 4 ) [B 5 O 8 (OH)](H 2 O) 2 based on the crystal-structure refinement. Single-crystal X-ray studies gave the space group P 2 1 /c, a 6.458(2), b 22.299(7), c 8.571(2) Å, β 103.047(13)°, V 1202.5(1.0) Å 3 , Z = 4. Structure refinement ( R 1 = 2.9%) revealed that two BO 4 tetrahedra and three BO 3 triangles share vertices to form B 5 O 10 (OH) units that link to other B 5 O 10 (OH) units along [100] and [001] to give a [B 5 O 8 (OH)] sheet parallel to (010). Within the central cavities of opposing sheets are the H 2 O groups, SO 4 tetrahedra, and Na (1) sites; the Sr and Na (2) sites occupy the interstices of a given sheet. The region of the structure where opposing cusps of neighboring sheets approach each other is dominated by weaker H-bonding associated with the OH and H 2 O groups, in accord with the observed perfect {010} cleavage. The strongest lines in the powder X-ray diffraction pattern, obtained after profile fitting using the Le Bail method, are as follows [ d in Å ( I ) ( hkl )]: 11.1498 (100)(020), 3.3948 (8)(061), 3.3389 (20)(042), 3.1993, 3.1990 (10)(160, 1 42), 3.0458(10)(052), 3.0250(7)(220), 2.7500 (10)( 2 22,142), 2.3999 (8)(260), 2.2300, 2.2284(7)(0 10 0,222), 1.9241, 1.9237(7)(311, 2 24). The holotype is deposited in the mineralogy collection of the Royal Ontario Museum, 100 Queen's Park, Toronto, Ontario M5S 2C6, Canada, accession number M56745.