Silicates — feldspar group · Sourced PROFILE
Albite
NaAlSi₃O₈
A sodium plagioclase feldspar common in granites and pegmatites; at Dara-i-Pioz it is a major phase of a rare quartz–albite–aegirine rock.
AT A GLANCE
- Formula
- NaAlSi₃O₈
- Crystal system
- Triclinic
- Space group
- C1̄
- Mohs hardness
- 6–6.5
- Density
- 2.60–2.65 g/cm³
- Optical character
- Biaxial (+) for low albite; biaxial (−) for high albite
CRYSTALLOGRAPHY
Crystal form & structure
Crystals commonly tabular on {010}, up to 3 cm; also divergent aggregates, granular or cleavable masses. Repeated (polysynthetic) twinning often shows as fine striations.
HAND-SAMPLE PROPERTIES
Physical properties
- Cleavage
- Perfect on {001}, very good on {010}, imperfect on {110}
- Fracture
- Uneven to conchoidal
- Tenacity
- Brittle
- Streak
- White
- Luster
- Vitreous, typically pearly on cleavages
- Transparency
- Transparent to translucent
- Observed colours
- White to grey, bluish, greenish or reddish; may be chatoyant
LIGHT & OPTICS
Optical properties
- Optical class
- Biaxial (+) for low albite; biaxial (−) for high albite
- Refractive index
- nα 1.526–1.530; nβ 1.531–1.533; nγ 1.534–1.541
- Fluorescence & electrical behaviour
- No diagnostic fluorescence is reported in the cited profile.
GEOLOGICAL SETTING
Formation
A major constituent of granites, granite pegmatites and some basalts; also forms in hydrothermal and alpine veins, low-temperature metamorphic rocks and sediments.
MINERAL COMPANY
Common associations
Quartz, orthoclase, muscovite, biotite and hornblende
FIELD NOTES
How to identify it
White colour, two good cleavages at nearly right angles, hardness 6–6.5 and fine twin striations separate it from quartz; distinguishing it from other feldspars needs optics or chemistry.
NAME & HISTORY
Where the name comes from
From the Latin albus, white, for its characteristic colour.
SCIENTIFIC SOURCE
Handbook of Mineralogy — Albite
External reference; factual profile paraphrased and attributed. Copyright remains with the publisher.
PROVENANCE
Documented occurrences
Dara-i-Pioz alkaline complex, Alai Range · Albite is a principal component, with quartz and aegirine, of a metasomatically altered alkaline rock that contains the rare minerals baratovite and miserite. The public record is intentionally limited to approximate locality.
Sourced · ApproximateLocality precisionThe mineralogy of a unique baratovite- and miserite-bearing quartz–albite–aegirine rock from the Dara-i-Pioz Complex