Ca₆Al₂(SO₄)₂B(OH)₄(OH,O)₁₂.26H₂O

This sample of charlesite is displayed in the Smithsonian Museum of Natural History. Charlesite is a sulfate mineral that contains calcium, aluminum and boron with the composition Ca₆Al₂(SO₄)₂B(OH)₄(OH,O)₁₂.26H₂O. The sample at left is about 3 cm across and is from the Kalahari manganese field, Cape Province, South Africa.