n in commerce. They never equal the
fine sapphire in their color, being more steely. They, of course, lack
dichroism and are softer than sapphire as well as lighter.

3. Blue tourmalines are never of fine sapphire blue. The name indicolite
which mineralogists give to these blue stones suggests the indigo-blue
color which they afford. The marked dichroism of tourmaline will also
help detect it. Some tourmalines from Brazil are of a lighter shade of
blue and are sometimes called "Brazilian sapphires."

4. Blue topaz is usually of a pale sky blue or greenish blue and is
likely to be confused with beryl of similar color. The high density of
topaz (3.53) as compared with beryl (2.74) serves best to distinguish
it.

"FANCY" BLUE DIAMONDS. 5. Blue diamonds are usually of very pale bluish
or violet tint. A few deeper blue stones are seen occasionally as
"fancy" diamonds. These are seldom as deep blue as pale sapphires. Even
the famous Hope Blue Diamond, a stone of about forty-four carats and of
great value, is said to be too light in color to be considered a fine
sapphire blue. Some of the deeper blue diamonds have a steely cast. The
so-called blue-white stones are rarely blue in their body color, but
rather are so nearly white that the blue parts of the spectra which they
produce are very much in evidence, thus causing them to face up blue.
There is little likelihood of mistaking a bluish diamond for any other
stone on account of the "fire" and the adamantine luster of the diamond.

6. Blue zircon, however, has nearly adamantine luster and considerable
fire. The color is usually sky blue. Such stones are seldom met with in
the trade.

For a more detailed account of the various blue stones see G. F.
Herbert-Smith's _Gem-Stones_, as follows:

For sapphires, pp. 172-173, 176, 182; for spinel, pp. 203, 204, 205; for
tourmaline, pp. 220, 221, 223; for topaz, pp. 198, 200, 201; for
diamond, pp. 130, 136, 170, and for zircon, pp. 229, 231.

LESSON XIV

COLOR--_Concluded_

PINK, PURPLE, BROWN, AND COLORLESS STONES

PINK STONES. Pink stones are yielded by (1) corundum (pink sapphire),
(2) spinel (balas ruby), (3) tourmaline (rubellite), (4) true topaz
(almost always artificially altered), (5) beryl (morganite), (6)
spodumene (kunzite), and (7) quartz (rose-quartz).

These pink minerals are not easily differentiated by color alone, as the
depth and quality of the pink vary greatly in different specimens of the
same