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GOLD AND GEMS
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ign of the cubes are distinct, however, from what is met with in the diamond.
And
after consideration of all the obaerved characters of these crystals it
will be seen that the explanation of the occurrence of the crystals in
the interior of a mass of iron by means of pseudomorphism is untenable.
Though the easy frangibility, the absence of evidence of cleavage, the
hollowness, and the occasionally crust-like structure, are more or less
characteristic of pseudo-morphic crystals, they are not incompatible
with an independent crystallization: on the other hand while the
superior hardness distinguishes the crystals from those of native
terrestrial graphite, the separatenass, completeness, and general
excellence of the crystals, the delicacy of various acicular'.-
projections, and more especially of the obtuse, almost flat, square
pyramid seen on some of the cube-faces, are sufficient to -prove that
the crystalline form never had a previous tenant. The delicacy of the
acicular projections is such that the crystals must have been formed in situ. In
case of pseudomorphism, the elements of the original mineral ought to
be in the vicinity of the crystals, and there ought to be an excess
either of the original mineral or of the replacing amorphous graphitic
carbon : both are, however, conspicuous by their absence, and in this
fragment of the iron the whole of the graphitic carbon is present as
cubic crystals.
On
examination of a large graphite nodule from the Coeke County meteoric
iron, now in the British Museum, crystals of graphitic carbon,
cubo-octahedral in form, are to be seen in some of the crevices.
There
can be absolutely no doubt that the graphitic crystals are the result
of crystallization of the meteoric graphite, and that they represent a
third allotropic condition of crystallized carbon, the general
characters being those of graphite, and the crystalline system that of
the diamond.
As
this form of graphitic carbon is unknown among terrestrial minerals,
and has so important a bearing on the formation of meteoric graphite,
it may conveniently receive a special name ; I suggest the term
"cliftonite," after Prof. R. B. Clifton, f.r.s., who has long been interested in the physical characters of minerals, and has done much to encourage their study.
A
full description of the meteoric iron itself and of the graphite
crystals will appear in the forthcoming number of the journal of the
Mineralogical Society.—L. Fletcher.—Nature.
Meteoric Graphite : a Link between Charcoal, Terrestrial Graphite, .and the Diamond.—We give above a curious paper on graphite of meteoric origin. The writer of scientific gossip in the Melbourne Leader thus notices this substance which has come to our globe from the realms of space :—
It
is well-known that graphite is a form of carbon intermediate between
charcoal and the diamond, and a curious link between the three has just
been discovered. Graphite has heretofore been regarded as amorphous ;
but Mx. Fletcher, while analysing some fragments of, a mass of meteoric
iron which fell in Western Australia, made the discovery that the
graphite contained in it was csystallised and of the same form as the
diamond. It is not known that any similar mineral exists anywhere -pn
the face of the earth, and rnuch curiosity is felt as to how the
charcoal of the meteorite became crystallised. The .meteoric graphite
is harder than the terrestrial article, although there is very little
difference in density, color, and streak. The question has been asked
whether meteoric graphite may not be a new allotropic form of carbon,
and no answer to the question has yet been given—there is merely a
probability that this may be the case. It is a tempting speculation to
imagine that the meteoric graphite is in a state of transition, and
that the crystallisation in cubes shows that it is more allied to the
diamond than to the usual form of. graphite. Looking to the softness
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