Albite

Albite is the sodic end member of both the plagioclase feldspar series and the alkali feldspar series.

If you have trouble remembering the name of the white feldspar and you’re at all familiar with Harry Potter, think of Albus Dumbledore, whose first name, Albus,  is Latin for white. (Seriously. That’s helped a surprising number of people keep their feldspars straight.)

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 NaAlSi3O8
Class Tectosilicate
3D frameworks of linked tetrahedra
Crystal system Triclinic
Habit Prismatic
Tabular
Bladed
Color White
Grey
Green
Hardness 6
Specific gravity 2.62
Cleavage Perfect(001), good (010), poor {110}
Fracture Uneven
Luster Pearly
Vitreous
Transparency Translucent
Streak White
Optical Properties
PPL Colorless
Non-pleochroic
Low relief
XPL 1st order greys
Polysynthetic/albite twinning (“zebra stripes”)
δ 0.011
Twinning Polysynethetic/albite
Pericline
after Perkins, 308-309

Albite in Hand Sample

Albite

More albite

Scanning electron micrograph

Albite in Thin Section

Thin Section GigaPans

Albite in diorite, plane polars

Albite in diorite, crossed polars

Polysynthetic twinning in albite, plane polars

Polysynthetic twinning in albite, crossed polars

Albite, PPL

Albite, XPL

Polysynthetic twinning

There is no corresponding photo or video for polysynthetic twinning in plane polars because the twinning isn’t visible in plane polars.

Further Reading

Albite at webmineral.com

Albite at mindat.org