III.—Note on Duporthite, a new Asbestiform Mineral

Extract

This mineral occurs in fibrous masses occupying fissures or shrinkage cracks in the serpentine of Duporth, near St. Austell, Cornwall. The thickest veins I have seen are not more than 1 1/2 inches. The fibres are placed transversely across the vein, making generally an angle with the walls of about 70°, so that the crystallization is probably oblique.

The mineral is greenish to brownish gray, has a silky lustre, H about 2 and Sp. Gr. 2.78 : insoluble in HCl, but the iron and magnesia are slowly dissolved out.

Thin fibres are flexible like asbestos. Heated in a matrass the mineral gives off a little water, and becomes lighter coloured ; in forceps thin fibres fuse to a dark glass in the hottest part of the flame. The spectroscope shews the sodium and calcium lines distinctly, but no trace of potassium or lithium.