If the star corundum is blue it is a star-sapphire, if red a star-ruby, and so on
Star-sapphires are very plentiful in the New England district of this
Colony, although usually of too dark colour for cutting purposes.
These gems are best cut en cabochon, care being taken to get the centre of the star in the middle of the convex surface.
It
is only of late years that these star stones have come into fashion in
Europe. Not many years ago they could have been purchased in Ceylon for
small sums, but star rubies at the present time, if of good quality,
fetch high prices ; being rare they are highly prized.
In
the Hope collection there were six asterias of a very high character.
Of course, the value of these gems is determined by their size and
quality. Star sapphires range from £2 to £100; star rubies are still
more valuable.
Besides
the ornamental uses to which these gems are put, there is that of the
more important one in connection with manufacture. That this item of
consumption is not an insignificant one, may be judged from the fact
that in the United States of America, where the watch industry is of
great magnitude, the consumption of gems alone for the jewelled works
of the watches manufactured in that country, cannot be less than
12,000,000 annually, of which nearly half are rubies and sapphires, the
remainder being principally garnets. The consumption, too, of " bort,"
used in the drilling and working of these gems, reaches many thousand
carats per annum.
It
is, of course, not necessary that these gems be of large size, but it
is important that they be free from flaws, of good colour, transparent,
and of the correct hardness.
In
the New England district of this Colony, sapphires are plentiful, and
although, unfortunately, many are very dark and opaque, yet very many
bright, clear gems may be gathered of good colour, transparent, and
correct hardness. Many of these transparent corundums, too, are of a
green colour (inferior Oriental emeralds), and these should not be
discarded. As the greater part of the gems used in America for
watch-making purposes are imported, and the whole of those used in
England, the collection of these gems is a matter worthy of some
consideration.
Simple Forms of the Hexagonal System.
As
all the varieties of corundum crystallize in the hexagonal system, it
will be as well to consider the most simple of the forms belonging to
it.
In
this system (unlike all the others) there are four axes; one, the
principal, has no fixed length, the remaining three lie at right angles
to the principal axis in one plane, and they are inclined to each other
at an angle at 60 degrees. This plane, by joining the three axes, forms
a hexagon, these axes being all the same length.
The primary form of this system is the hexagonal pyramid (two
six-sided pyramids placed base to base), all the other forms being
derived from it. In this form the principal axis joins the two
six-sided solid angles (refer to the cubical system in the article
diamond for the meaning of terms), the lateral axes joining the lateral
solid angles if belonging to the first order, and the centre of the
lateral edges if belonging to the second order. (These orders are only
of importance in combinations.) It has twelve faces, these being
isosceles triangles, and they are acute or obtuse as the principal axis
is long or short. This is a common form of the corundum.
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