: Classified as a “tectosilicate” in some recent Mineralogy texts.
: Hexagonal, Colorless in thin section but thick grains show weak
colors and pleochroism, prismatic crystals, hexagonal in cross section, moderate relief, n
> b, weak birefringence, Uniaxial negative, lengthfast.
: c- elongated.
: Common in granitic pegmatites, usually as an accessory mineral. Also in
granites and syenites.
: Hexagonal, blue, green, yellow, or pink in thin section, depending
on composition; strongly pleochroic with maximum absorption in the direction of
when c axis is parallel to the analyzer direction since it is a negative mineral), hexagonal
in cross section, high relief, n > b, strong birefringence, Uniaxial negative, lengthfast.