No strictly scientific classification of precious stones is possible. Those in the Townshend collection have been described in the same order as that adopted in chapter vii. It so happens that the diamond, as consisting of the pure element carbon, takes for every reason the first place; while the sapphire and ruby, as varieties of corundum, the oxide of aluminium, naturally fall into the second position. Other species are grouped roughly in accordance with some prominent constituent:
| Characteristic element. | ||
| Carbon | Diamond. | |
| Aluminium | Corundum, spinel, turquoise, topaz, tourmaline, garnet. | |
| Magnesium | Peridot. | |
| Glucinum | Beryl, chrysoberyl, phenakite, euclase. | |
| Ziconium | Zircon. | |
| Silicon | Opal, quartz, iolite, moonstone. | |
There are, as might have been expected, some stones unrepresented in the Townshend collection. Amongst these may be named—Alexandrite, Axinite, green garnet or Demantoid, Spessartite, Odontolite, Phenakite, Spodumene, and Sphene. Any one interested in precious stones should, after inspecting the Townshend collection, turn to the general collection of rings in the museum. The beautifully and curiously cut diamond in a ring found at Petersham (No. 780—1904); the two Indian thumb-rings of white jade (1022 and 1023—1871); the Persian turquoise with gold-inlays (965—1871); and the two fine bloodstones, (735 and 749—1871) are specially noticeable.
