These samples of crocidolite are displayed in the Smithsonian Museum of Natural History. Crocidolite is one of the silicate minerals of magnesium and iron which form the fibrous materials collectively labeled asbestos. It has the composition Na₂(Fe,Mg)₃Fe₂Si₈O₂₂(OH)₂. Crocidolite is a variety of the mineral riebeckite. The sample at left is about 15 cm across and is from Carn Brea mine, Prieska district, Cape Province, South Africa.

This sample of the crocidolite variety of riebeckite is from Todos Santos, Cochabamba, Bolivia. The center bundle is about 25 cm high.

These two samples typify what is called "blue asbestos", which is notorious for its attributed risk of lung cancer for those who are exposed. In particular, there is a large body of literature about the health hazards of South African blue asbestos.