Epifanovite, NaCaCu5(PO4)4[AsO2(OH)2] • 7H2O: a New Mineral from the Kester Deposit, Sakha (Yakutia) Republic, Russia

Epifanovite, NaCaCu5(PO4)(4)[AsO2(OH)(2)] <bold> </bold>7H(2)O, a new natural copper, sodium and calcium arsenate-phosphate, has been found in a quartz-phosphate pocket within greisenized cassiterite-bearing granodiorite of the Kester tin deposit, Sakha (Yakutia) Republic, Russia. The mineral occurs as crusts of tabular pseudotetragonal crystals up to 50 m across and 10 m thick. Associated minerals are fluorapatite, pseudomalachite, malachite, a Na-analogue of batagayite, tobermorite, libethenite, arsenolite, native copper and unknown Mg-Zn phosphate. Epifanovite is turquoise-blue with pale blue streak, vitreous luster (dull in crusts), and a Mohs hardness of 3. The mineral is brittle. Cleavage is perfect on (001) and good on (100) and (010). Density measured in the Clerici solution is 3.65(3) g/cm(3); the calculated density is 3.73 g/cm(3). Epifanovite is optically biaxial (-), = 1.708(5), = 1.730(5), = 1.735(5). 2Vobs = 40 degrees-45 degrees, 2V(calc) = 50 degrees. Optical orientation: X = a, Y = b. The empirical formula calculated on the basis of P + As = 5 is (Na0.94K0.06)sigma(1.00)(Ca0.82Na0.08)sigma(0.90)(Cu5.04Zn0.06)sigma(5.10)(PO4)(4)[(As0.81P0.19)sigma(1.00)(O1.92OH2.06Cl0.02)sigma(4.00)] <bold> </bold>7.37H(2)O. The idealized formula is NaCaCu5(PO4)(4)[AsO2(OH)(2)] <bold> </bold>7H(2)O. The Raman spectrum contains the following bands, cm(-1): 293, 359 ((1-2), CuO5); 455, 556, 594, 640, 921, 962, 1002, 1086, 1153 ((1-4), PO4), 77, 121, 161, 183, 730, 828, 858 ((1-3), AsO4), 2900, 3200, 3410 ((1), OH). The mineral is monoclinic, P2(1)/m, a = 9.6912(9), b = 9.7440(9), c = 9.9561(9) angstrom, = 102.23 (1)degrees, V = 918.7(1) angstrom(3), Z = 2. The strongest reflections in the powder X-ray diffraction pattern are, I-d angstrom-hkl: 100-9.73-001, 35-6.79-110, 12-4.355-021, 43-3.072-130, 24-3.061-221, 24-3.003-222, 11-2.698-023, 10-1.6775-504. The mineral was named in honor of the Russian geologist Porphyry Prokop'evich Epifanov, who discovered the Ege-Khaya and Kester tin deposits. Epifanovite is structurally close to the lavendulan-group minerals and related species: andyrobertsite, calcioandyrobertsite, mahnertite and richelsdorfite.