opal /ˈopəl/
 蛋白石,貓眼石
 O·pal n.  Min. A mineral consisting, like quartz, of silica, but inferior to quartz in hardness and specific gravity.
 Note: ☞ The precious opal presents a peculiar play of colors of delicate tints, and is highly esteemed as a gem.  One kind, with a varied play of color in a reddish ground, is called the harlequin opal.  The fire opal has colors like the red and yellow of flame.  Common opal has a milky appearance.  Menilite is a brown impure variety, occurring in concretions at Menilmontant, near Paris.  Other varieties are cacholong, girasol, hyalite, and geyserite.
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 opal
      n : a translucent mineral consisting of hydrated silica of
          variable color; some varieties are used as gemstones