REDEFINITION OF THE LINDACKERITE - NEW CH EMICAL FORMULA AND NEW CRYSTALLOGRAPHICAL, OPTICAL-DATA

Lindackerite, an inadequately described mineral, has been redefined (d ecision of the CNMMN 9 january 1995) and the correct data of the miner al are presented here. Revised chemical formula is: (Cu,Co)(5)(AsO4)(2 )(AsO3 . OH)(2) . 10H(2)O. It is the Cu equivalent of geigerite. The m ineral is triclinic with a = 8.035(2), b = 10.368(4), c = 6.453(2)Angs trom, alpha = 79,60(3), beta = 84,83(3), gamma = 86,17(3)degrees, spac e group P1 or P1, V = 525.9(2)Angstrom(3) and Z = 1. The calculated de nsity is 3.37 g/cm(3). The strongest lines in the X-ray diffraction pa ttern are: 10,2(100)(010); 8,02(70)(100); 5,158(30)(101); 4,001(40)(12 1)(200); 3,668(60)(121)(021)(210); 3,264(30)(201); 3,154(60)(211); 3,0 64(40)(220)(211)(112); 2,923(30)(022)((1) over bar 31); 2,665(50)(300) (112)(122); 2,613(40)(212)(310). Optically it is biaxial (+) with 2V(m eas.) = 74 degrees, 2V(calc.) = 72 degrees, alpha = 1,632(2), beta = 1 ,662(2), gamma = 1,725(5) at 590 nm. Dispersion r<v is strong. Optical orientation is beta boolean AND a = 21,3 degrees on {010}, beta boole an AND a = 34,4 degrees on {001}.