Fontarnauite, (Na,K) (sub 2) (Sr,Ca)(SO (sub 4) )[B (sub 5) O (sub 8) (OH)](H (sub 2) O) (sub 2) , a new sulfate-borate mineral from Doganlar (Emet), Kutahya Province, western Anatolia, Turkey

Fontarnauite was discovered in cores recovered from the Kutahya-Emet 2 and 188 (named here as Doganlar) boreholes drilled in the Emet borate basin near the village of Doganlar, Kutahya Province, Western Anatolia, Turkey. The Emet (or Emet-Hisarcik) 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 (sub calc) = 2.533 g/cm (super 3) The new mineral is optically biaxial (-), alpha 1.517(2), beta 1.539(2), gamma 1.543(2) (590 nm); 2V (sub meas) = 46(1) degrees ; 2V (sub calc) = 46 degrees ; X^a 95.0 degrees (beta obtuse); Y//b, Z^c 81.9 degrees (beta 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 (sub 3) 17.75, B (sub 2) O (sub 3) 38.66, CaO 2.26, SrO 18.98, Na (sub 2) O 12.65, K (sub 2) O 1.70, H (sub 2) O 10.01, total 102.01 wt.%. The empirical formula (based on 15 O atoms per formula unit) is (Na (sub 1.84) K (sub 0.16) ) (sub Sigma 2.00) (Sr (sub 0.82) Ca (sub 0.18) ) (sub Sigma 1.00) S (sub 1.00) B (sub 5) H (sub 5) O (sub 15) ; the endmember formula is Na (sub 2) Sr(SO (sub 4) ) [B (sub 5) O (sub 8) (OH)](H (sub 2) O) (sub 2) based on the crystal-structure refinement. Single-crystal X-ray studies gave the space group P2 (sub 1) /c, a 6.458(2), b 22.299(7), c 8.571(2) A, beta 103.047(13) degrees , V 1202.5(1.0) A (super 3) , Z = 4. Structure refinement (R1 = 2.9%) revealed that two BO (sub 4) tetrahedra and three BO (sub 3) triangles share vertices to form B (sub 5) O (sub 10) (OH) units that link to other B (sub 5) O (sub 10) (OH) units along [100] and [001] to give a [B (sub 5) O (sub 8) (OH)] sheet parallel to (010). Within the central cavities of opposing sheets are the H (sub 2) O groups, SO (sub 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 (sub 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 A (I) (hkl)]: 11.1498 (100)(020), 3.3948 (8)(061), 3.3389 (20)(042), 3.1993, 3.1990 (10)(160,142), 3.0458(10)(052), 3.0250(7)(220), 2.7500 (10)(222,142), 2.3999 (8)(260), 2.2300, 2.2284(7)(0 10 0,222), 1.9241, 1.9237(7)(311,224). 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