Portal logo
186            PRECIOUS STONES
6.  Ruby and Tourmaline (Red)
The red tourmaline is occasionally so nearly ruby-red in color as to necessitate care. The dichroism of the tourmaline is very similar to that of the ruby, but stronger. The color is not so deep nor the lustre so great, but it is often more transparent than the ruby. The test of hardness is sufficient, also specific gravity.
Hardness. Specific Gravity.
Ruby...................................9            3.9 to 4.1
Tourmaline.............................7.25        3.08
7.  Spinel and Tourmaline (Red)
The dichroiscope will decide between these, as the spinel is singly refractive, the tourmaline strongly doubly refractive, and the latter lacks any yellow tint.
8. Tourmaline (Red) and Topaz (Red)
If the eye fails to distinguish between the rose-pink red of the tourmaline and the denser yellowish to brownish red of the topaz, hardness, specific gravity, or the dichroiscope will do so. One of the twin colors of the topaz is yellow.
Hardness. Specific Gravity.                    Dichroism.
Topaz.........8            3.50103.56         Red and yellow.
Tourmaline... .7.25         3.08                   Rose and dark red.
9. Sapphire (Blue) and Tourmaline (Blue)
These may be distinguished by the quality of color. Whatever the shade of color in the sapphire, from corn-flower to indigo, it is always clearly blue. The tourmaline blue in­clines to green. Under the dichroiscope this is reversed, the twin colors of the sapphire being dark blue and a light green­ish blue, those of the tourmaline light and dark blue.
Either of the other tests is sufficient to establish identity.
Hardness. Specific Gravity.
Sapphire................................9             3.9 to 4.1
Tourmaline...... ......................7.25        3.1