is a member of the Feldspar Group of minerals that also
Andesine, Anorthite, Bytownite, Hyalophane, Labradorite,
Oligoclase, Orthoclase, Sanidine
and Sunstone. Moonstone
is a popular name for Orthoclase and/or Plagioclase
Feldspar showing a blue sheen. The blue sheen is produced by the
presence of very finely dispersed Albite crystals
or plates within a body of Orthoclase or Labradorite. This
blue sheen is refered to as adularescence. Blue sheen
Moonstone with a colorless and transparent body free
of inclusions makes for a rare and beautiful gem. Common Moonstone is usually
translucent to opaque or heavily included.
gets its name from its blueish glow due to adularescence.
The name Orthoclase
is from the Greek words orthos meaning right
and kalo meaning I cleave because
its cleavages are at right angles. Feldspar is from the Swedish feldt + spat
meaning that it was found in fields overlying granite.