one another and
reflecting the light. The minute furrows containing translucent
carbonate of lime, produce a series of more or less brilliant colours,
according to the angle at which the light falls upon them. Occasionally
some of the finest pearls are found loose in the shell. As many as one
hundred pearls have been found in one oyster, but of little or no
value. The pearls of the young oyster are yellow, and in the older
oyster are of a pinkish hue.
The Use of Pearl-shells.—The
pearl-shells shipped from Australia to the United States and Europe are
used principally for the manufacture of knife-handles, shirt-buttons,
&c* Considerable quantities are also used tor papier-m&chg, and
other ornamental work. The pearl buttons, shirt-studs* &co, now
made in the United States, are said to be the best and cheapest in the
world, a fact due in great measure to the care used in selecting the
material and to the improved methods of cutting.—Field.
---------,---------------------_------
CUBIC CRYSTALS OF GRAPHITIC CARBON.
In
the analysis of a meteoric iron found in 1884 i" the sub-district of
Youndegin, Western Australia, and of which two of the four fragments
have been generously presented to the British Museum by the Rev.
Charles G. Nicolay, Curator of the Geological Museum, Fremantfc, I have
obtained some crystals, a description of which may be of interest to
the students of carbon.
The
crystals were obtained as an insoluble residue on treatment of 8*3200
grammes of the iron with aqua regia : they are bright, opaque,
grayish-black, have a metallic lustre, and present forms belonging to
the cubic system. As their characters were not recognized as belonging
to any known mineral, it seemed unlikely that the nature of the
crystals could be completely determined, seeing that the total weight
obtained was only 3 milligrammes: further, two fragments of the iron,
weighing 2 and 7 grammes respectively, had not yielded a single
crystal, and there was thus a possibility of their being so localized
in the iron as to render im-. practicable an increase of the quantity
of material available for experiment. : The crystals were about a
hundred in number, the average thickness of the larger ones being 1/100
of an inch. Many of them are sharply defined cubes; some have their
edges truncated by the faces of the dodecahedron ; in others the edges
are replaced by rounded faces of a tetrakishexahedron.
Their
hardness is greater than that of rock salt and less than that of
calcite: the streak is black and shining. Of four crystals, two sank to
the bottom and two remained near the surface of a solution having a
specific gravity of 2.12. The crystals are unaffected by acids; heated
in a combustion-tube in a current 01 oxygen, hydrogen, or chlorine,
they are un-attacked even when the glass begins to melt. Heated in a
platinum capsule wifh the table-blowpipe, they slowly disappear without
flame. Heated with potassium nitrate in a crucible over a Bunsen
burner, they are unaltered; but disappear very slowly, without
deflagration, when heated with the table-blowpipe.
In
density, colour, and streak, and in its chemical behaviour, the
residual mineral thus bears a close resemblance to native graphite, but
it is considerably harder, and it presents itself in well-defined
crystals which belong, like those of the other crystallized form of
carbon, the diamond, to the cubic system : terrestrial graphite, when
crystallized, is found only as tabular crystals so indistinctly formed
that doubt has long existed as to whether they should be referred to
the hexagonal or monosymmetric system.
in
a paper entitled " Graphite pseudomorphous after Iron Pyrites, "
Haidinger, in 1846, described some graphitic crystals which were
doubtless
* The large mother-o'-pearl shells are now meant, but the writer confuses the two species.—Compilers.
