AUGITE AND HORNBLENDE. 



367 



CHLORITE. 



Augite and Hornblende in Metamorphic Rocks. 



The varieties of augite and their alteration products are frequently 

 met with, though they are scarcely so important as the minerals of 

 the hornblende group. Crystalline or granular limestone is rich in 

 the paler coloured varieties of both minerals. Malacolite, which is a 

 white or blue variety of augite, forms layers in the limestone of Loch 

 iS hi n, in Sutherland, crystals often being a foot long. The limestone 

 of Totaig, which is embedded in micaceous gneiss, is full of nodules 

 of it. It is found in the limestone of Glen Tilt, and near Serpentine 

 in the hills of Coyle, in Aberdeenshire. The sap-green variety of 

 sahlite is often associated with malacolite. Sahlite is well known 

 from the marble of .Tiree, which is characterised by numerous minute 

 crystals of the dark-green variety, about the size of shot. Another 

 of these augitic minerals is coccolite, of a deep rich green colour. 

 Diallage is recorded from the diallage rock of Unst, in Shetland, 

 where the crystalline masses of diallage are embedded in fine 

 granular labradorite. It is also recorded by Professor James Geikie 

 at Pinbain, near Lendalfoot, in Ayrshire. True augite does not 

 occur in the metamorphic rocks of Scotland, though it is found in 

 the volcanic rocks of Rum and Skye. 



Augite and hornblende, in Scotland, are both connected witli the 

 formation of serpentine. Heddle states that the serpentines of Unst, 

 in Shetland, are derived from diallage ; that one of the beds to the 

 west of Portsoy is derived from gabbro, and the other from eupotide ; 

 while the bed to the east of Portsoy is derived from an augitic rock. 

 The same author states that a bed of serpentine in the Farrid Head, 

 Sutherland, is unquestionably derived from gneissic schists. 



Among hornblendic minerals asbestos is plentiful in the granular 



