#opal  a translucent mineral consisting of hydrated silica of variable color; some varieties are used as gemstones
  supertype:  #mineral  #opaque_gem
  subtype:  #black_opal__blackopal  a dark colored opal with internal reflections of green or red
  subtype:  #fire_opal__girasol  an opal with flaming orange and yellow and red colors
  subtype:  #harlequin_opal__harlequinopal  a reddish opal with small patches of brilliant color

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