minerals Article Pickeringite from the Stone Town Nature Reserve in Ci˛e˙zkowice(the Outer Carpathians, Poland) Mariola Marszałek * , Adam Gaweł and Adam Włodek Department of Mineralogy, Petrography and Geochemistry, AGH University of Science and Technology, al. Mickiewicza 30, 30-059 Kraków, Poland;
[email protected] (A.G.);
[email protected] (A.W.) * Correspondence:
[email protected] Received: 26 January 2020; Accepted: 17 February 2020; Published: 19 February 2020 Abstract: Pickeringite, ideally MgAl (SO ) 22H O, is a member of the halotrichite group minerals 2 4 4· 2 XAl (SO ) 22H O that form extensive solid solutions along the joints of the X = Fe-Mg-Mn-Zn. 2 4 4· 2 The few comprehensive reports on natural halotrichites indicate their genesis to be mainly the low-pH oxidation of pyrite or other sulfides in the Al-rich environments of weathering rock-forming aluminosilicates. Pickeringite discussed here occurs within the efflorescences on sandstones from the Stone Town Nature Reserve in Ci˛e˙zkowice(the Polish Outer Carpathians), being most probably the first find on such rocks in Poland. This paper presents mineralogical and geochemical characteristics of the pickeringite (based on SEM-EDS, XRPD, EPMA and RS methods) and suggests its possible origin. It belongs to the pickeringite–apjohnite (Mg-Mn joints) series and has the calculated formula Mg Mn Zn Cu Al (S O ) 22H O (based on 16O and 22H O). The unit cell 0.75 0.21 0.02 0.01 2.02 0.99 to 1.00 4 4· 2 2 parameters refined for the monoclinic system space group P21/c are: a = 6.1981(28) Å, b = 24.2963(117) 1 Å, c = 21.2517(184) Å and β = 100.304(65)◦.