A Note on the Nosean Phonolite of the Wolf Rock, Cornwall

Extract

The first systematic descriptions of the nosean phonolite of the Wolf Rock were given by Allport (Geol. Mag., 1871, p. 247; 1874, p. 462). Later a fuller account of the rock was provided by Teall in his British Petrography (1888, pp. 367–368). Since that time the rock has been repeatedly figured in text-books of petrography and in the light of two chemical analyses provided by J. A. Phillips (in Allport, 1871), regarded as a type example of a more sodic phonolite chemically comparable with the plutonic mariupolite. In view of the early date of these analyses, Mr. J. H. Scoon has at my request carried out a new analysis of the fresh rock, the results of which are provided in Table 1 (No. 1). This analysis reveals significant differences from the original, particularly in the potash content and shows that the rock is to be compared with the well-known phonolite of Brüx, Bohemia (Table 1, No. 3), and a phonolite from Colfax Co., New Mexico (Table 1, No. 2). The trace element distribution in the Wolf Rock has also been kindly determined for me by Dr. S. R. Nockolds (Table 1). Some additional mineralogical data which re-examination of the rock has provided may now be set down.