The mineralogy of the crocidolite (blue asbestos) veins at Wittenoom Gorge was examined to determine the cause of failure to recover soma of the fibre by the ore-dressing methods currently being practised. As a, result of this yamina.tion, several fo.Ctors pertinent to the problem were found to be a function of the pa.ragenosis of the veins. The occurrence of magnetite from tho'cap rock within the veins was thought to be preventing fiborisation during troo.tment. Several petrologic features are described and their relation to the ore genesis is discussed, Comparison with the crocidolite deposits of the Union of South Africa is also considered.