DOLERITE INTO HORNBLENDE-SCHIST. 135 



Andesine from Scourie Dyke *. 



SiO, 58-16 



Al,03 26-66 



CaO 5-79 



MgO -65 



jSXO 6-99 



K,0 1-76 



100-01 

 The recent work of Descloiseauxt appears to have placed beyond 

 doubt the independent existence of andesine. I now proceed to 

 describe in detail the lithological characters of the principal varieties 

 of rock. 



Dolerite (Diabase ?). The least modified specimens are dark in 

 colour and coarsely crystalline in texture. The augite grains and 

 crystals frequently measure 1 mm. across, and the felspars 2 mm. 

 X "5 mm. Three specific-gravity determinations made on samples 

 from different localities gave 3-106, 3-105, and 3-086. A bulk- 

 analysis of the rock yielded the following result J : — 



SiO, 47-45 



TiO, 1-47 



Al,03 14-83 



Fe,03 2-47 



FeO 14-71 



CaO 8-87 



MgO 5-00 



Kfi -99 



IsXO 2-97 



Kfi 1-00 



CO, -36 



100-12 



Under the microscope the rock is seen to consist of felspar, augite, 

 titaniferous magnetic iron-ore, apatite, and some secondary products, 

 including hornblende, chloritic minerals, quartz, and pyrites. The 

 secondary minerals, however, occur only in very small quantity. 



The felspar is usually present in lath-shaped sections of the type 

 common in dolerites and diabases ; but occasionally plates of felspar 

 having a polysynthetic structure may be recognized, in which the 

 individual portions are not bounded by any definite crystalline faces. 



In the freshest slides the felspar-sections are often perfectly limj^id, 

 bnt as a rule they show traces of alteration, and in some cases 



* Dr. Heddle gives four analyses of andesine in bis paper on the Scotch 

 felspars, Trans. Roy. Soe. Edin. xxviii. p. 246. 



t Bull. Soc. Min. France, July 1884. 



I PoOg and S (in FeS2) were not estimated. The P2O, is therefore reckoned 

 with Al2b3. The water was determined absolutely. There was a slight gain 

 on ignition, showing that the oxygen taken up by the FeO was more than 

 sufficient to counterbalance the loss due to expulsion of water &c. 



