N RESEMBLES YELLOW DIAMOND. Here we have less opportunity to
judge of the species by the color than was the case with the red
stones. The diamond, of course, is easy to tell, not by the kind of
yellow that it displays, for it varies greatly in that respect, but
rather by its prismatic play blended with the intrinsic color. Its
luster also gives an immediate clue to its identity. It is necessary,
however, to be sure that we are not being deceived by a yellow zircon,
for the latter has considerable "fire" and a keen luster. Its strong
double refraction and its relative softness, as well as its great
density will serve to distinguish it. Of the other yellow stones, the
true or precious topaz is frequently inclined to a pinkish or wine
yellow and many such stones lose all their yellow (retaining their pink)
when gently heated. The so-called "pinked" topazes are thus produced.

The yellow corundum rarely has a color that is at all distinctive. As
far as color goes the material might be yellow quartz, or yellow beryl,
or yellow zircon, or yellow tourmaline (Ceylon type). Many of the
yellowish tourmalines have a decidedly greenish cast (greenish-yellow
chrysoberyl might resemble these also). However, in general if one has a
yellow stone to determine it will be safer to make specific gravity or
hardness tests, or both, before deciding, rather than to rely upon
color.

LESSON XII

COLOR--_Continued_

GREEN STONES

Let us first consider what mineral species are most likely to give us
green stones. Omitting the semi-precious opaque or translucent stones we
have:

1. Grass-green beryl (the emerald) which is, of course, first in
value among the green stones and first in the fine quality of its
color.

2. Tourmaline (some specimens of which perhaps more nearly approach
the emerald than any other green stones).

3. The demantoid garnet (sometimes called "olivine" in the trade).

4. True olivine (the peridot and the chrysolite of the trade).

5. Bluish-green beryl (aquamarine).

6. Green sapphire (Oriental emerald or Oriental aquamarine).

7. Chrysoberyl (alexandrite and also the greenish-yellow
chrysoberyl).

1. Considering first the emerald, we have as legitimate a use of color
in distinguishing a stone as could be selected, for emerald of fine
grass-green color is not equaled by any other precious stone in the rich
velvety character of its color. We have to beware