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CHLORITIC MINERALS. 



Chlorites are essentially metamorphic minerals, and according to 

 Heddle, the true clilorites never occur in volcanic rocks, while the 

 saponites are confined to volcanic rocks. Chlorite has been found 

 in granite at Rubislaw and at Girdleness. The chlorites comprise 

 glauconite, talc chlorite, penninite, ripidolite, chlorite, and chloritoid. 

 They often have a cry ptocry stall ine structure, so that they are only 

 to be identified by chemical or external characters. Penninite is 

 found in serpentine in hornblendic gneiss in Scalpa, Harris, in the 

 mica schist of Glen Lochy, in Perthshire, and in Shetland. Ripi- 

 dolite is found in limestone, in mica slate, in chlorite slate, and in 

 hornblendic gneiss, especially at Cape Wrath. Chlorite is found in 

 serpentinous beds, in micaceous gneiss which is free from felspar. 

 It occurs in the mica slate which ranges from north-east to south-west 

 through the lower Highlands of Scotland, in granular limestone parallel 

 to the limestone of Glen Tilt, and in chlorite slate to the west of 

 Portsoy, in Banffshire. Chloritoid is a Shetland mineral, as is talc 

 chlorite ; both are found near Hillswick. 



The saponites comprise Delessite, chlorophseite, Hullite, saponite, 

 and seladonite. They may be regarded as decomposition products, 

 and in that sense as metamorphic, but there are no British meta- 

 morphic rocks, properly so called, in which they form an important 

 constituent. Delessite abounds about Dumbuck ; it has a dull lustre 

 and dark colour. A variety in the tufa at Elie Ness contains 5 per 

 cent, of soda and 3 per cent, of potash ; like saponite, it always con- 

 tains about 20 per cent, of manganese. Chlorophaeite, when fresh, 

 resembles a green jelly, when weathered it resembles drops of asphalt ; 

 it contains less alumina, the iron is chiefly ferric oxide, instead of 

 ferrous oxide ; the magnesia is reduced to one-half, and the water is 

 half as much again. Saponite is soft, greasy, green, and translucent ; 

 it is richer in silica and poor in alumina ; the iron is small in quantity 

 and the water large. The saponites are regarded as products of the 

 decomposition of augite and olivine. 



