Webster's English Dictionary

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zircon

zir.con \'z*r-.ka:n\ n [G, modif. of F jargon jargoon, zircon, fr. It 
   giargone] : a tetragonal mineral ZrSiO4 consisting of a zirconium silicate 
   and  occurring usu. in square prisms of adamantine luster and brown or 
   grayish color with transparent kinds esp. of reddish or brownish color 
   being used as gems