Opal

     Where does Precious Opal get those ever changing colors?  Believe it or not, the colors are a result of the silica crystals and spaces between them being evenly spaced, allowing the diffraction of light. 
     Common Opal, or "potch", is actually colorless because the silica are not sized correctly or spaced properly.  Most Mexican Opal do not have a show of colors and are therefore a Common Opal.  However, they often contain a single color and are seen as a solid and vibrant orange or red mass.  This variety of Mexican Opal is referred to as a Fire Opal.  
     There are many names for varieties of Precious Opal that are derived from their dominant colors, such as Rainbow Opal or Peacock's Tail Opal.  Other names for varieties of Opal are derived by the way light affects the colors, such as Contra Luz Opal whose "fire" is best viewed when the light source is behind and shining through the opal instead of being pointed at the surface.

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