A cleavage fragment of Oligoclase showing the typical twinning striations of
the Plagioclase Feldspars.
| SPECIES | % SODIUM | % CALCIUM | SPECIFIC GRAVITY | COLOR | OCCURRENCE |
| ALBITE | 100-90 | 0-10 | 2.60-2.65 | White to colorless | Granite pegmatites |
| OLIGOCLASE | 90-70 | 10-30 | 2.63-2.66 | White to slightly greenish to brownish | Monzonites, Granodiorites, also in granitic pegmatites |
| ANDESINE | 70-50 | 30-50 | 2.66-2.68 | Colorless to white to greenish yellow | Andesites and Diorites |
| LABRADORITE | 50-30 | 50-70 | 2.68-2.72 | Grayish, bluish, greenish with iridescence along cleavage planes | Both occur as small to large grains in gabbros and anorthosites. |
| BYTOWNITE | 30-10 | 70-90 | 2.72-2.74 | White to grayish | |
| ANORTHITE | 10-0 | 90-100 | 2.74-2.76 | White to grayish and reddish | Limestones that have undergone contact metamorphism |
CRYSTALLOGRAPHY - Triclinic
CRYSTAL GROWTH AND HABIT - The plagioclase feldspars typically form thin, tabular crystals. They are found also in large cleavable masses or they can be massive. Twinning is common producing striations that can be seen along cleavage faces.
HARDNESS 6 - 6.5
STREAK - White
BREAKABILITY - Cleavage is very good in 1 direction and good in another producing blocky fragments with angles of about 90o. This series of feldspars have and uneven fracture and are brittle.