1  definition  found 
 
  From  Webster's  Revised  Unabridged  Dictionary  (1913)  [web1913]: 
 
  Spinel  \Spi*nel"\,  Spinelle  \Spi*nelle"\,  n.  [F.  spinelle,  or 
  LL  spinellus  perhaps  from  L.  spina  a  thorn,  a  prickle,  in 
  allusion  to  its  pointed  crystals.]  (Min.) 
  A  mineral  occuring  in  octahedrons  of  great  hardness  and 
  various  colors,  as  red,  green,  blue,  brown,  and  black,  the 
  red  variety  being  the  gem  spinel  ruby.  It  consist  essentially 
  of  alumina  and  magnesia,  but  commonly  contains  iron  and 
  sometimes  also  chromium. 
 
  Note:  The  spinel  group  includes  spinel  proper,  also 
  magnetite,  chromite,  franklinite,  gahnite,  etc.,  all  of 
  which  may  be  regarded  as  composed  of  a  sesquioxide  and 
  a  protoxide  in  equal  proportions. 

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