Occurrence of a coarsely crystalline kaolin mineral in some south african fire-clays

Thin sections of fire-clays almost invariably show shreds and plates of colorless minerals, which although difficult to identify exactly, are almost certainly either dickite or members of the kaolinite-anauxite series. During a visit to a deposit of fire-clay at Boksburg, about 10 miles from Johannesburg, Dr. A. L. du Toit drew my attention to a buff colored clay, which contained “nodules” of an opaline looking material. These “nodules” range up to 1 cm. in length and are sometimes fairly well rounded although more usually somewhat elliptical. The material is flesh colored and easily scratched by a knife.