Sodalite is a scarce mineral that can be rock forming.
Sodalite is named in reference to its sodium content.
It is used for carvings and some jewelry pieces. Its
light to dark pure blue color is well known in the semi-precious
stone trade. Sodalite is a member of the feldspathoid
group of minerals. Minerals whose chemistries are close
to that of the alkali feldspars but are poor in silica
(SiO2) content, are called feldspathoids. As a result
or more correctly as a function of the fact, they are
found in silica poor rocks containing other silica poor
minerals and no quartz. If quartz were present when
the melt was crystallizing, it would react with any
feldspathoids and form a feldspar.. Localities that
have feldspathoids are few but some produce large quantities
of sodalite. Sodalite, when not blue, is hard to distinguish
from other feldspathoids. It is the only feldspathoid
that contains chlorine. Sodalite dissolved in a dilute
solution of HNO3 gives a positive chlorine test obtained
from some swimming pool test kits.