28 iiOTÔ : notes on the geolog"ï- 



APATITE. 



Apatite occurs in the Doleritic or Anamesitic rocks iii the 

 form of extremely fine needles, devoid of terminal faces, 

 being colourless, and always traversed by transversal fissures. 

 Its crystals sink almost to a minimum size, and are not, com- 

 paratively speaking, so large as those found in the typical 

 European Dolerites ; and for this reason they might be easily 

 mistaken for the microlites of felspar which often resolves from 

 the poles of a larger crystals in Basalts. The apatite is typi- 

 cally found in the three slides only, which are in my pos- 

 sesion (Kippai and Hoko), and both are magnetite (not ilmenite)- 

 bearing rocks. The crystals are dark-margined, owing to the 

 total reflection of light on the prismatic faces ; and sometimes a 

 single brown-coloured axis entirely or partially runs through the 

 crystal. A grey or light-brown variety, so often found in An- 

 désites, is entirely absent, though a dark-brown crystal of an 

 apatite-like mineral was once observed with strong absorj)tion 

 parallel to the prismatic axis. The sure criterion of the presence 

 of apatite can only be found in its hexagonal cross-section. 



ANA WIME AND NATROLITE. 



A cave-rock in the southern Gio-ô, presents an anomalous 

 habit ; a slide made of it contains a colourless mineral in angular 

 or polygonal interspaces between the crystals of plagioclase 

 {PL II, Fig. 5). It shows no signs of any crystallographic face, 

 nor cleavage, but only has a frittered appearance, being traversed 

 with irregular cracks, and also being pierced through in all 

 directions with the needles of apatite which is excessively rich 



