It sounds demented, or robotic, but it’s neither. A demantoid is a green form of garnet found only on the western slopes of the Ural Mountains of Russia.
from The American Heritage® Dictionary of the English Language, 4th Edition:
n. A transparent, green variety of garnet used as a gem.
from Wiktionary, Creative Commons Attribution/Share-Alike License
n. a green garnet
from the GNU version of the Collaborative International Dictionary of English
n. A yellow-green, transparent variety of garnet found in the Urals. It is valued as a gem because of its brilliancy of luster, whence the name.
from The Century Dictionary and Cyclopedia
n. A light-green to emerald-green variety of garnet, found in the Ural mountains. It is transparent and of brilliant luster, and is classed as a gem.
from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.
n. a green andradite used as a gemstone