86 PROFESSOR HEDDLE ON THE MINERALOGY OF SCOTLAND. 
unusually tough hand-and-foot scramble ; but when the difficulties special to 
carrying heavy overbalancing hammers,—breaking rocks where there is little 
foothold,—and when that which is grasped is readily set upon the move,—be 
considered, it will not be wondered at that MaccuLtocu’s mineral has never yet 
been analysed. 
It moreover occurs in very small amount; it would take many days’ work 
to obtain a sufficiency of the perfectly unaltered green mineral. The writer in 
three days’ hard work obtained a sufficiency of what was either perfectly or 
moderately fresh. 
To the excellent description of Maccuttocy I can add nothing, except to 
emphasize some of his statements regarding that which is the most singular 
property of this mineral,—namely, the extreme rapidity with which it changes 
in colour when first exposed. From “the transparent yellow-green of the finest 
olivine ” sometimes in the space of ten minutes it passes to a dark green-black ; 
and in other specimens from the fine brown-orange of cinnamonstone to the 
rich brown and brilliant jetty-lustre of asphalt. By instantly after fracture 
wrapping up the one-half of an olive specimen tightly in repeated folds of paper, 
and keeping it as far as possible from exposure to air, heat, and light, I managed 
to retain the colour for about three weeks, only to see it lose it in half an hour 
when finally exposed. The other half became perfectly black after less than 
an hour’s exposure. 
Dr Maccuttoc# has noticed it scaling off in concentric crusts ; the finest 
piece I obtained showed, when first broken, layers of successive depositions, 
some very light, some dark green; this specimen could not at first have been 
distinguished from the celadonite which will be noticed as occurring at Tayport, 
in Fife. During ten minutes’ exposure to sunlight this specimen, which at first 
was rather dull, had assumed a lustre like that of obsidian; it had become in 
some of the layers dark green, in others black, and it had rent through the 
whole thickness of its layers into rude hexagonal prisms. 
Specimens securely bottled wp immediately upon extraction from the rock 
gave on analysis very little more of ferrous oxide than those which had been 
freely exposed ; the change of colour therefore is not due to peroxidation of 
the ferrous oxide, but must be due to molecular change ; and BrewstER* has 
stated that he has optically determined that it is due to the mineral splitting up 
into a multitude of minute hexagonal prisms. 
The material which I analysed was broken out of rude basaltic pillars; some 
of it, perhaps one-fifth, was green when placed in the bottles; none had changed 
further than to be rich asphalt brown, and this was still vitreous in lustre. It 
finally withers into a rusty brown or yellow friable lustreless powder. 
The specimen was analysed ten days only after having been collected. 
* Reference lost. 
