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A cave in granitic rocks was studied in Mezesse, South Cameroon. Coralloid speleothems, draperies and dissolution traces on the cave walls attest to its truly karstic nature. The speleothems consist of microlayers of opal and taranakite (K,NH₄)Al₃(PO₄)₃(OH).9H₂O. They indicate a significant mobilization of silica, Al and K from granite during the formation of the cave. Identification of silicified bacteria in the speleothems layers suggests a possible role of these micro‐organisms in silica deposition. The presence of taranakite and of silicified organic remains within the speleothems lead to a better understanding of the genesis of the cave.