Sanidine

In thin section, alkali feldspar grains often look like they’re sprinkled with dirt (PPL) or tiny confetti (XPL). You can find the explanation on the alkali feldspar page.

Physical Properties
Chemical formula (K,Na)Si3O8
Class Tectosilicate
3D framework of linked tetrahedra
Crystal system Monoclinic
Habit Prismatic
Tabular
Elongate
Often have square cross section
Color White
Variable
Hardness 6
Specific gravity 2.56
Cleavage Perfect (001), good (010)
Luster Vitreous
Transparency Transparent to translucent
Streak White
Optical Properties
PPL Colorless
Low relief
XPL 1st order grey
δ 0.007
Twinning Carlsbad
Manebach
Baveno
after Perkins, 307

Further Reading

Sanidine at webmineral.com

Sanidine at mindat.org