192 PRECIOUS STONES
distinguish
them. The bottle-green chrysoberyl, or alexandrite, is known by its
red color under artificial light. The diopside and tourmaline are more
plentiful and very similar. As they are in this color sometimes almost
identical in appearance, it is best when uncertain to put them to one
of the usual tests.
Hardness. Specific Gravity. Dichroism.
Sapphire.....9 3.9 to 4.1 Decided ; green and brown.
Chrysoberyl. .8.5 3.68103.78 Strong ; green, yellow, red.
Zircon.......7.5 4.6 to 4.7 Very weak, scarcely discernible.
Tourmaline .. 7.25 3.1 Strong ; yellow and bluish green.
Diopside.....6 3.2 to 3.3 Weak.
26. Epidote, Vesuvianite, Sphene, Apatite, Andalusite, Fluorite, and Dioptase (in Green)
Sphene
in this color shows decided tints of yellow, green, and reddish brown
under the dichroiscope. Dioptase is not quite clear, and is a very deep
green. For the distinguishing marks of the others, refer to No. 24.
27. Emerald and Demantoid
These
can scarcely be mistaken for each other, as the admixture of yellow in
the green of demantoid (commercial olivine) is very marked. It is not,
however, so discernible at night, when the color often appears to be
the true emerald-green.
