Lapis Lazuli (Arabic-latin - blue stone) is made up of several minerals - if only
is small quantities (augite, calcite, dioposide, mica, haüynite, hornblende,
pyrite). Some experts say that it is not a mineral, but a rock; the main
ingredient is lazurite.
Lapis Lazuli doesn't like pressure, high temperatures, hot baths, acids,
and alkalis 
. It has vitreous to greasy luster. The best quality is striped or
spotted. White Calcite protrusions, in Chilean and Russian stones, diminishes value.
Well Distributed pyrite is advantageous and is taken to show genuineness. Too
much pyrite causes a dull, greenish tint.