This is a 'preproof' accepted article for Mineralogical Magazine. This version may be subject to change during the production process. DOI: 10.1180/mgm.2020.45 Ammoniotinsleyite, (NH 4 )Al 2 (PO 4 ) 2 (OH)·2H 2 O, a new mineral species from the guano deposit at Pabellón de Pica, Iquique Province, Chile NIKITA V. CHUKANOV 1,2* , GERHARD MÖHN 3 , IGOR V. PEKOV 2 , NATALIA V. ZUBKOVA 2 , DMITRY A. KSENOFONTOV 2 , DMITRY I. BELAKOVSKIY 4 , SVETLANA A. VOZCHIKOVA 1 , SERGEY N. BRITVIN 5 , AND JOY DESOR 6 1 Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Moscow region, 142432 Russia 2 Faculty of Geology, Moscow State University, Vorobievy Gory, Moscow, 119991 Russia 3 Dr.-J.-Wittemannstrasse 5, 65527 Niedernhausen, Germany 4 Fersman Mineralogical Museum of the Russian Academy of Sciences, Leninsky Prospekt 8-2, Moscow, 119071 Russia 5 Department of Crystallography, St Petersburg State University, Universitetskaya Nab. 7/9, 199034 St Petersburg, Russia 6 Im Langenfeld 4, 61350 Bad Homburg, Germany *E-mail: chukanov@icp.ac.ru Running title: Ammoniotinsleyite, a new mineral