Staurotide

The cruciform variety of this mineral has already appeared in this work; in the description of it, mention is made of the substance occuring in Scotland: British Mineralogy being concluded without a figure of it, I have added one here, along with the red kind in single crystals, from St. Gothard; it is the dark grey specimen: I am indebted to the Rev. P. Forbes for it, who found it in Mica slate at Boharm, in Elginshire. The same gentleman favoured me with some masses of Cyanite, from the same place, in which were a few minute crystals of Staurotide of a red colour, and transparent like that from St. Gothard; the masses also contained Quartz, Mica, and decomposing Feldspar. St. Gothard has hitherto produced the most perfect specimens, as the crystals in them are sharply defined with various modifications upon their ends; have some transparency and a clear colour. The cruciform variety on the other hand often exhibits larger crystals, but they are rough, and of a dull colour, being mixed with the substance of the rock they arc imbedded in, which is a grey micacious slate (see tab. IX) The grey specimen from Scotland presents a still less pure variety, which retains none of the red colour of the unmixed substance, and in which the crystals are thin and badly defined . they do not appear to cross each other ID pairs, but run in all directions through the Mica slate they occur in. Crossed crystals of Staurotide have been found by Dr. Fitton, in a micaceous compound at Glenmalur lead mines, in the county of Wicklow,^* but.it does not appear to be common.

An enlarged figure of two crystals, with wedge-shaped terminations, crossing each other obliquely, is added at the bottom of the plate from a specimen found in Brittany.