150 km E of Windhoek. 4,5 km long cave system. Mined for bat guano. A white friable slag with arnhemite, pyrocoproite and pyrophosphite (all three names published without IMA approval) is interpreted to have resulted from the melting of ashes during the combustion of bat guano.
Ref.:
Martini, J. E. (1994): Two new minerals originated from bat guano combustion in Arnhem Cave, Namibia. South African Speleological Assoc. Bull. 33, 66-69. [Abstract in Am. Mineral. 84, 193]