26 Rocks of Noyang. 



shades of bright green. The ores of iron, and perhaps also 

 titanium, which are removed in the alteration of the mica, 

 are not always redeposited in rectangular crystals or in 

 granular masses. I have observed frequently in these chlorite 

 pseuclomorphs, that the magnetite (? titanic iron) has been 

 placed in the basal plane as opaque black needles, either 

 singly or in tufts or masses. It is very common for these 

 needles to be arranged in more or less well-marked stellate 

 groups, with rays in eluding angles of approximately, or exactly, 

 30°. Such arrangements are only visible in sections parallel 

 to the cleavage, while in sections perpendicular to it the 

 needles only show as horizontally-arranged tufts. 



The chlorite either fills almost exactly the space formerly 

 occupied by the magnesia-iron-mica or amphibole in the less 

 altered rocks, or in those which have been most altered it fills 

 irregular spaces with cleavable or with radial masses. In 

 many instances flakes of a chloritic mineral are to be found 

 throughout the whole rock. 



In selecting a sample of rock from which to extract the 

 chloritic mineral for examination, I necessarily had to 

 choose one in which the process of chloritisation from mica 

 might be considered to be complete. This involved a partly 

 decomposed condition of the rock generally; and I found, 

 probably in consequence of this, that the selected mineral, 

 although carefully extracted and examined under the lens, 

 still contained impurities. 



The chloritic mineral formed pseudomorphs after mica 

 (probably haughtonite). Its hardness is 1*5 to 2', specific 

 gravity 2785. Its colour is dark green, with a rather pearly 

 lustre in the cleavage plates, and the streak is grey, with a 

 tinge of green. Before the blowpipe it fuses at the edges of 

 thin flakes to a black magnetic glass, and is decomposed easily 

 by sulphuric acid and by hot hydrochloric acid, white scales 

 of silica being set free. In every example which I examined 

 in the process of selection I found minute portions of a 

 colourless mineral so intimately mixed with the mass as not 

 to be separable. 



One of the crystals of which I prepared a basal cleavage 

 plate as a microscopic object showed these two different 

 minerals distinctly. One I observed to be green in colour, 

 and of the character which I have described when speaking 

 of the chloritic pseudomorphs after mica ; the other a colour- 

 less radiating mineral, apparently monoclinic. There was 



