SUNSTONE (Oligoclase)
  from Oregon (the bit at the bottom is no longer in my possession - but it is a nice example of rough sunstone) |
A member of the plagioclase feldspar series, oligoclase forms as tabular crystals, which are commonly twinned. It forms in many igneous and metamorphic rocks. The variety used in jewellery is called sunstone or, less commonly, aventurine feldspar. It can be found in the USA, Norway, India, the former USSR and Canada.
Hardness: 6