Andalusite

The grey variety ot Andalusite has scarcely been noticed, except by Dr. Blake as mentioned by Dr. Fitton in the Geological Transactions: the specimens discovered by him at Killiney in Mica Slate were in part internally of the characteristic red colour, and some of them are scopiform. The substance I have figured as Corundum, from near Aberdeen, possessed the characters of the Andalusite from the Forez which the Count de Bournon first described, as Spath adamantin d’un rouge violet; I allowed myself to be guided by great authority, therefore, could connect it with nothing but Corundum, from which it is now admitted to be distinct. Kirwans Petrilite seems to have remained in obscurity, until Dr. Fitton, after examining the Leskean collection, made it known that it is what Werner has since called Andalusite, and that Karsten was the first discoverer of it calling it, Wurflicher (Cubic) Feldspath.

Such specimens as the two upper ones here figured I have repeatedly received from Aberdeenshire; they are worn pieces of micaceous Schistus, in which are imbedded grey rectangular prisms much harder than the rock; the fracture of these prisms, parallel to their sides, is laminated, slightly glistening, across them it is splintery. They are infusible. I have been puzzled much by them, but considering the grey variety of Adalusite, of Killiney, is intermediate between them and the red, it seems proper that they should be included under the same species.

Below is figured a specimen of micaceous Schistus containing similar prisms but much softer, and more allied to the black parts of the crystals of Macle. They seem to strengthen Mr. Stephen’s supposition, that there is a connection between these two minerals, an idea that receives some additional strength from the tubular form sometimes assumed by the Andalusite, as formerly observed in Brit. Min. 1. p. 145, the similar position of the laminæ and the variable degrees of hardness of the two substances. It is much to be wished that comparative analyses were made. I would observe, that the measures given formerly by me, are incorrect, being taken upon rounded or modified faces, and not from the fracture, which produces a rectangular prism.