Copper-Tiu Veins of th«i Akénobé District. 17 



minute fissures in the rock. It is clearly of secondary infiltration 

 .as the lack of a cataclastic structure suggests. 



Akenobeite, a leucocrate differentiated from the diorite magma. 

 At Higashiyama, about 500 meters northeast of the village of 

 Akénobé, a leucocratic rock in the form of a small boss, or 

 apophysis, is exposed in close association with diorite. It lies 

 adjacent to the outcrop of the abandoned copper-tin vein of 

 Higashiyama. In the field it is clear that it represents a leucocrate 

 differentiated from the diorite magma. 



The rock in question is medium-gi*ained in texture, the chief 

 component, feldspar, often measuring 3 mm. or more in length. 

 Usually being very poor in ferromagnesian minerals, it is pure 

 white or very light coloured. 



Under the microscope, it shows a unique structure. It is 

 composed essentially of thick tabular idiomorphic and hyp- 

 idiomorphic crystals of feldspar in confused aggi'egation, the 

 interstices between them being filled with an aggregate of fine 

 grains of quartz (PI. IV., Figs. 3, 4). Two kinds of feldspar 

 are distinguished, namely, oligoclase and orthoclase. The charac- 

 teristic narrow polysynthetic twin-lamellae easily distinguish the 

 oligoclase from the orthoclase, which occurs usually in simple 

 crystals or in Karlsbad twins. The plagioclase always exceeds the 

 orthoclase. They are all characterized by the indices of refraction, 

 being lower than the adjoining quartz, and are more or less 

 kaoUnized and turbid. The quartz filling the interstices between the 

 feldspars is rather small in amount. Sometimes the feldspars are 

 more or less corroded along their margins, and invaded along the 

 cracks by the quartz. The quartz is easily distinguished from the 

 feldspars by its freshness and positive uniaxial character. Femic 

 constituents play a very subordinate part in this rock. Biotite, 



