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Any of several varieties of compact earthy clay (impure halloysite), usually 
red, yellow, or brown because of the presence of iron oxide, and consisting 
essentially of hydrous silicates of aluminum or less often of magnesium. It is 
a waxy decomposition product of basaltic rocks, having the variable composition 
of lateritic clays. Syn: [[bolar]]

Source: Dictionary of Mining, Mineral, and Related Terms

[[Category: Geology]]