Antipinite, KNa (sub 3) Cu (sub 2) (C (sub 2) O (sub 4) ) (sub 4) , a new mineral species from a guano deposit at Pabellon de Pica, Chile

The new oxalate mineral antipinite is found in a guano deposit located on the Pabellon de Pica Mountain, Iquique Province, Tarapaca Region, Chile. Associated minerals are halite, salammoniac, chanabayaite, joanneumite and clays. Antipinite occurs as blue, imperfect, short prismatic crystals up to 0.1 mmX0.1 mmX0.15 mm in size, as well as their clusters and random aggregates. The mineral is brittle. Mohs hardness is 2; D (sub meas) =2.53(3), D (sub calc) =2.549 g cm (super -3) . The infrared spectrum shows the presence of oxalate anions and the absence of absorptions associated with H (sub 2) O molecules, C-H bonds, CO (sub 3) (super 2-) , NO (sub 3) (super -) and OH-ions. Antipinite is optically biaxial (+), alpha =1.432(3), beta =1.530(1), gamma =1.698(5), 2V (sub meas) =75(10) degrees , 2V (sub calc) =82 degrees . The chemical composition (electron-microprobe data, C measured by gas chromatography of products of ignition at 1200 degrees C, wt.%) is Na (sub 2) O 15.95, K (sub 2) O 5.65, CuO 27.34, C (sub 2) O (sub 3) 48.64, total 99.58. The empirical formula is K (sub 0.96) Na (sub 3.04) Cu (sub 2.03) (C (sub 2.00) O (sub 4) ) (sub 4) and the idealized formula is KNa (sub 3) Cu (sub 2) (C (sub 2) O (sub 4) ) (sub 4) . The crystal structure was solved and refined to R=0.033 based upon 4085 unique reflections with I>2sigma (I). Antipinite is triclinic, space group P1, a=7.1574(5), b=10.7099(8), c=11.1320(8) Aa, alpha =113.093(1), beta =101.294(1), gamma =90.335(1) degrees , V=766.51(3) Aa (super 3) , Z=2. The strongest reflections of the powder X-ray diffraction pattern [d, Aa (I,%)(hkl)] are 5.22 (40)(111), 3.47 (100)(032), 3.39 (80) (210), 3.01 (30)(033, 220), 2.543 (40)(122, 034, 104), 2.481 (30)(213), 2.315 (30)(143, 310), 1.629 (30)(146, 414, 243, 160).