This is a 'preproof' accepted article for Mineralogical Magazine. This version may be subject to change during the production process. DOI: 10.1180/mgm.2022.60 Saccoite, Ca 2 Mn +3 2 F(OH) 8 ·0.5(SO 4 ), a new, microporous mineral from the Kalahari Manganese Fields, South Africa Gerald Giester 1 *, Christian L. Lengauer 1 , Chutimun Chanmuang N. 1 , Dan Topa 2 , Jens Gutzmer 3 and Karl-Ludwig von Bezing 4 1 Institut für Mineralogie und Kristallographie, Universität Wien - Geozentrum, Josef- Holaubek-Platz 2, 1090 Wien, Austria; 2 Naturhistorisches Museum Wien, Burgring 7, 1010 Vienna, Austria; 3 Helmholtz Institute Freiberg for Resource Technology, Bergakademie Freiberg, Brennhausgasse 14, 09599 Freiberg, Germany; 4 19 Wolseley Street, Kimberley 8301, RSA * Author for correspondence: Gerald Giester, Email: gerald.giester@univie.ac.at Abstract Saccoite, Ca 2 Mn 3+ 2 F(OH) 8 ·0.5(SO 4 ), is a new mineral found at the N’Chwaning III mine, Kalahari Manganese Fields, Northern Cape Province, Republic of South Africa. It occurs as fillings of gangues and voids in hydrothermally altered manganese ore (bixbyite) and barite. Further associated minor minerals are braunite, gypsum, chlorite, sturmanite, and ettringite. Saccoite forms small needles, felted crystal masses or crusts. The new mineral is olive green,