s therefore not a green corundum
(Oriental emerald) as the latter has hardness 9 and scratches topaz.

With hardness evidently between 7 and 8 and with double refraction and
with the kind of flaws peculiar to rather brittle minerals we had in all
probability either a tourmaline or an emerald.

DICHROISM. The dichroscope (which might have been used much earlier in
the test but was not at hand at the time) was next tried and the stone
was seen to have marked dichroism--a bluish green and a yellowish green
appearing in the two squares of the instrument when the stone was held
in front of the opening and viewed against a strong light.

As either tourmaline or emerald might thus exhibit dichroism (the
tourmaline more strongly, however, than the emerald) one more test was
tried to finally decide the matter.

SPECIFIC GRAVITY. The stone was removed from its setting and two
specific gravity determinations made by means of a specific gravity
bottle and a fine chemical balance. The two results, which came closely
alike, averaged 2.70 which agrees very nearly with emerald (2.74) and
which is far removed from the specific gravity of tourmaline (3.10). The
stone was now _definitely known_ to be an emerald, as each of several
tests agreed with the properties of emerald, namely:

Color--nearly grass green.

Imperfections--like those of emerald.

Hardness--7-1/2.

Refraction--double.

Dichroism--easily noted.

Specific gravity--2.70.

While one who was accustomed to deal in fine emeralds might not need to
make as detailed an examination of the stone as has just been indicated
above, yet for most of us who do not have many opportunities of studying
valuable emeralds it is safer to make sure by complete tests.

One other concrete example of how to go about testing unknown stones
must suffice to conclude this lesson, after which the student, who has
mastered the separate lessons preceding this, should proceed to test as
many "unknowns" as his time and industry permit in order to really make
_his own_ the matter of these lessons. It may be added here that the
task of testing a stone is much more rapid than this laborious effort to
teach others how to do it might indicate. To one skilled in these
matters only a few seconds are required for the inspection of a stone
with the lens, the dichroscope, or the refractometer, and hardness
tests are swiftly made. A specific gravity test requires more time and
s