Oligoclase

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

Physical Properties
Chemical formula (Na,Ca)(Si,Al)4O8
Class Tectosilicate
3D framework of linked tetrahedra
Crystal system Triclinic
Habit Prismatic
Tabular
Elongate
Columnar
Grainy
Massive
from minerals.net
Color Colorless
Brown
Greenish
Grey
Yellowish
Hardness 7
Specific gravity 2.65
Cleavage Perfect {001}, Good {010}
Fracture Uneven
Luster Vitreous
Transparency Transparent to translucent
Streak White
Optical Properties
PPL Coloress
Non-pleochroic
XPL 1st order grey
δ 0.009
after webmineral.com

Further Reading

Oligoclase at mindat.org

Oligoclase at webmineral.com