Albite

Albites
  • Albite from Crete
General
Categoryplagioclase, feldspar, tectosilicate
Formula
(repeating unit)
NaAlSi
3
O
8
or Na
1.0–0.9
Ca
0.0–0.1
Al
1.0–1.1
Si
3.0–2.9
O
8
IMA symbolAb[1]
Strunz classification9.FA.35
Crystal systemTriclinic
Crystal class
Space groupC1
Unit cell
  • a = 8.16, b = 12.87
  • c = 7.11 [Å]; α = 93.45°
  • β = 116.4°, γ = 90.28°; Z = 4
Identification
ColorWhite to gray, blueish, greenish, reddish; may be chatoyant
Crystal habitCrystals commonly tabular, divergent aggregates, granular, cleavable massive
TwinningCommon giving polysynthetic striae on {001} or {010} also contact, simple and multiple
CleavagePerfect on {001}, very good on {010}, imperfect on {110}
FractureUneven to conchoidal
TenacityBrittle
Mohs scale hardness6–6.5
LusterVitreous, typically pearly on cleavages
StreakWhite
DiaphaneityTransparent to translucent
Specific gravity2.60–2.65
Optical propertiesBiaxial (+)
Refractive index
  • nα = 1.528–1.533
  • nβ = 1.532–1.537
  • nγ = 1.538–1.542
Birefringenceδ = 0.010
2V angle85–90° (low); 52–54° (high)
Dispersionr < v weak
Melting point1,100–1,120 °C (2,010–2,050 °F)
Other characteristicsLow- and high-temperature structural modifications are recognized
References[2][3][4]

Albite is a plagioclase feldspar mineral. It is the sodium endmember of the plagioclase solid solution series. It represents a plagioclase with less than 10% anorthite content. The pure albite endmember has the formula NaAlSi
3
O
8
. It is a tectosilicate. Its color is usually pure white, hence its name from Latin, albus.[5] It is a common constituent in felsic rocks.

  1. ^ Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". Mineralogical Magazine. 85 (3): 291–320. Bibcode:2021MinM...85..291W. doi:10.1180/mgm.2021.43. S2CID 235729616.
  2. ^ Handbook of Mineralogy
  3. ^ Mindat.org
  4. ^ Webmineral data
  5. ^  One or more of the preceding sentences incorporates text from a publication now in the public domainChisholm, Hugh, ed. (1911). "Albite". Encyclopædia Britannica (11th ed.). Cambridge University Press.