None occurred within ten years of first exposure to crocidolite. One formula given for crocidolite is NaFeFeSiO(OH). It is formed by the alteration of crocidolite. It occurs in banded iron formations as the asbestiform variety "crocidolite" (blue asbestos). Crocidolite (blue asbestos), commonly used in high temperature applications. Blue quartz contains inclusions of fibrous magnesio-riebeckite or crocidolite. Minerals mined in Kuruman include Manganese, Iron Ore, Tiger's eye and Crocidolite. Amosite, crocidolite, tremolite, anthophyllite and actinolite are members of the amphibole class. SV40 may act as a co-carcinogen with crocidolite asbestos to cause mesothelioma. A classic example is tiger's eye quartz, crocidolite asbestos replaced by silica. Crocidolite commonly occurs as soft friable fibers. Some World War II gas masks contained chrysotile asbestos or crocidolite asbestos in their filters. The richest deposits of Crocidolite in the world are found in the Kuruman district. Block B, Block C, and Block D were contaminated with friable crocidolite asbestos. Glaucophane, crocidolite, riebeckite and arfvedsonite form a somewhat special group of alkali-amphiboles.