It has long been known that several of the felspar-porphyry dykes (Elvans) of the West of Cornwall contain crystals of pinite--apparently pseudomorphous after iolite--as an accessory mineral, and similar crystals occur.in the granite in several places.

In the parish of Breage there are several of these dykes running towards the sea in a south-easterly direction, which are somewhat largely used as road-material. That which reaches the sea at Praa is in places thickly charged with the pinite crystals, and the same in a somewhat less degree may be said of the dyke which passes from the village of Trew through Great Wheal Fortune.