Rb may be lamprophyres, kimberlites or other rare ultramafic, potassic or ultrapotassic rocks. It can be described as a mafic phonolite or a potassic tephrite. Holocene layers contain augitite, leucite basanite, potassic hawaiite and leucite tephrite. Associating minerals are aegirine, arfvedsonite, eudialyte, nepheline, potassic feldspar, and sodalite. In terms of chemistry, the BVG are moderate to highly potassic calk-alkaline in type. Significant porphyry-style mineralisation is won from highly potassic to ultrapotassic granites. Potassic basanite and limburgite are found in the Pleistocene layers. Pink-colored potassic migmatite is found in veins within the rock. Augitite, potassic limburgite, pyroxene trachybasalts and trachyte-andesite are found in the Pliocene layers. There are two distinct varieties&colon; "potassic liver of sulfur" and "ammoniacal liver of sulfur".