57 



TAB. CCCXXXIIL 



Sienite. 



Class 1. Earths. Order 2. Aggregate. 



Gen. Petuntse. Spec. Sienite. 



1 his, 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 Horn- 

 blende ; 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 Porphyrinic Gra- 

 nite ; 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. 



