The Collaborative International Dictionary of English v.0.48:

Aventurine \A*ven"tu*rine\, n. [F. aventurine: cf. It.
   avventurino.]
   1. A kind of glass, containing gold-colored spangles. It was
      produced in the first place by the accidental (par
      aventure) dropping of some brass filings into a pot of
      melted glass.
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   2. (Min.) A variety of translucent quartz, spangled
      throughout with scales of yellow mica.
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   Aventurine feldspar, a variety of oligoclase with internal
      firelike reflections due to the presence of minute
      crystals, probably of hematite; sunstone.
      [1913 Webster]