Sienite

This, although very different in appearance from what is to be expected in Sienite, agrees as to the ingredients, especially as being composed chiefly of Feldspar and Hornblende; the latter being more or less in partly formed black Crystals. The Feldspar is grey with a blue iridescence, which is better conceived than figured. The iridescent faces of the Red Feldspar sometimes possess this lustre most beautifully; and I have specimens which I picked up in the road in my neighbourhood, which I suppose to be more rare than the present, which I purchased at the late museum at Yarmouth, as brought from near Aberdeen in Scotland. This is, according to some, a Porphyritic Granite; the Feldspar being relieved by the dark ground gives it a porphyritic appearance.

This is sometimes called Scotch Labradore Stone, on account of the iridescence, which is of the same nature in the grey Feldspar of Labradore, though they are much more brilliant and varied in their colours.