These garnets are often sold as olivines; they are heavier than olivines and softer.
Demantoide is composed of:
| Silica | 35.44 |
| Lime | 32.85 |
| Sesquioxide of iron | 32.85 |
| Magnesia | .20 |
Topaz.
Topaz belongs to the rhombic system of crystallization. Its cleavage is basal and perfect, fracture uneven, hardness 8, scratching quartz distinctly, specific gravity 3.4 to 3.6, lustre vitreous, refraction double, and colors ranging from colorless or white to bluish-white, light blue, wine-yellow, straw-yellow, golden-yellow, greenish- and pale-red to pink.
Topaz becomes electric from rubbing or pressure, and retains electricity for twenty-four hours. Before the blow-pipe topaz partly loses color, but does not melt, and with borax it fuses slowly to a white bead.
Topaz is partially attacked by sulphuric acid, and dissolves in salts of phosphorus.
The composition of topaz is:
| Silicon | 15.05 |
| Aluminium | 30.02 |
| Oxygen | 36.08 |
| Fluorine | 17.05 |
Goutte d’eau or colorless topaz, sometimes called “slaves diamond,” Siberian or bluish-white, Brazilian or golden to reddish-yellow, Saxony or pale-wine yellow, Brazilian ruby or pink, Brazilian sapphire or light blue, and aquamarine or greenish, are the various commercial names for topaz.