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226 NATURAL HISTORY OF PRECIOUS STONES, &c.
fire,
whence they were called "Acausti," applies exclusively to the Ruby.
For whilst the Garnet easily fuses into a dark globule of oxide of iron
(and in some Swedish mines constitutes, in its coarsest form, an
appreciable proportion of the ore smelted), Henckel relates an
experiment in which a Buby was sufficiently softened by means of a
powerful burning-glass to receive the impression from a Jasper
intaglio, without the slightest detriment to its original colour or
hardness on its cooling.
The
same conclusion may be deduced from the brief notice in Theophrastus,
who particularises, amongst the " polygonal " ones found in the
neighbourhood of Miletus, some having "six" angles. Now the numerous
angles of the common Garnet, a rhombic dodecahedron, form its most
distinguishing feature ; whilst the Spinel Buby is a perfect
octahedron, and therefore presents but six angles : and the exactness
of its singular form would naturally fix the attention of the early
mineralogist. Pliny gives the first place to the Carbunculi
Amethystizontes, " in which the extreme blaze goes out in the purple of
the Amethyst." These may have been our Almandines, as well as our
purple Spinels, for the difference between the two is hardly to be
appreciated by the eye alone.
But
the true Buby and its two inferior varieties can with greater certainty
be referred to that class of the Carbunculi described separately by
Pliny as the Lychnis. His Lychnis belonged to the same family
of fiery stones as the Carbunculus, was of pre-eminent beauty, and
derived its name from its property either of lighting up lamps, or of
lighting up itself by lamplight (a lucernarum ac-censu). The former
explanation of his meaning is supported by Orpheus, saying of his
Lychnis ι
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