MENACHANITE IN MICACEOUS SCHIST. J7 



nail, though they cannot be detached in large scales. These 

 laminae, in pieces fresh broken, have a silk}' lustre ; and in 

 some places they areas finely striated, as if they were formed 

 of fibres united longitudinally. The latter characteristic 

 and their colour disappear in pieces that have been exposed 

 to the air; un ochrey yellow, a blackish tint, and a gray, 

 mingling together, and destroying the primitive colour. 



Particles of mica are seen glistening on some parts of the 

 rock: but, beside these detached scales disseminated through 

 the rock, this mineral exists in it in a state of extreme at- 

 tenuation, for it produces the silvery lustre, which covers 

 the surface of the stone as with a varnish. 



An examination of this schist gave me no indication of 

 mechanite, except the black colour, which sometimes spread 

 through the interior of the rock, and indicated a kind of de- 

 composition ; but hitherto my observations furnished me 

 with nothing beyond simple conjecture. 



The formation of an artificial lake above the wood ofAcutinthe 

 Grirnaldi, having required a perpendicular cut in the moun- ^JJ^d some 

 tain, afforded me a favourable opportunity of pushing my parts of the 

 inquiries farther. I then observed a kind of stratification in of decomposi- 

 the mountain ; but the strata are so disordered, that it is im- tion and con- 

 possible to ascertain their general direction. Some veins of gjaJJSJ men *" 

 quartz run in the direction of the strata themselves. The 

 black colour, which I had already observed extends into the 

 substance of the schist, mixes with a yellow ochre, which 

 fills the cavities produced by the decomposition of the stone, 

 I examined these cavities with a- lens in places where the 

 black colour was deepest, and found that this colour Was 

 produced by a pulverulent substance, in shining, angular 

 grains, attracted by the magnet, and in short exhibiting all 

 the mineralogical characters of menachanite. 



From the pieces of schist, which I had broken off from perfectly re. 

 the mountain, I selected some, that exhibited throughout ^mtl oa the* 

 large spots of this black substance, mixed with the yellow- shore, 

 ish ochre I have described. These I powdered in a mortar ; 

 and from this powder the magnet separated several grains 

 of menachanite perfectly resembling that on the shore of 

 Sestri and Pegli. 



Vol. XX VI. —June, 1810. II Thus 



