A deep blue, usually
opaque mineral, which makes up part of the lazurite in the gem
lapis lazuli but is also used by itself as a
gemstone. It was first discovered in
Greenland (where it was incorrectly thought to be a type of
feldspar) and did not become popular until after large deposits were discovered in
Ontario and a large stone was given to
Princess Margaret of
England by her husband. (Hence the alternate name
princess marble.) It's usually made into beads or
cabochons or polished and used as an
inlay.