Albite-Anorthite series | SSHADE

Mineral phase

IMA name: Albite-Anorthite series

Name and identifiers

Secondary names: Plagioclase feldspar

Class: silicate mineral
Compound type: tektosilicate
Comments: Plagioclase is a wider series $(Na,Ca)(Si,Al)_4O_8$ of the feldspar group

Compositional phase diagram of the different minerals of the feldspar solid solution (Wikipedia - By Muskid - Own work, CC BY-SA 4.0)

Chemical composition

Formula: $(Na,Ca)(Al,Si)AlSi_2O_8$
Chemical formula: ((Na)x(Ca)1-x)((Al)1-x(Si)x)AlSi2O8
Elemental formula: (Na)0-1 (Ca)0-1 (Al)1-2 (Si)2-3 O8
Isotope mixture type: terrestrial abundance

	Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$Na$	Sodium	element	0 - 1		constituent element	main
	$Ca$	Calcium	element	0 - 1		constituent element	main
	$Al$	Aluminium	element	1 - 2		constituent element	main
	$Si$	Silicon	element	2 - 3		constituent element	main
	$O$	Oxygen	element	8		constituent element	main

Composition comments: Common replacement: K (limited solid solution) - Common impurities: Ti, Fe, Mg, H2O

Oxides composition

Oxides

Formula	$Na_{2}O$	$CaO$	$K_{2}O$	$Al_{2}O_{3}$	$SiO_{2}$
Mass fraction (%)

Classifications

Strunz

Class: silicates (09)
Division: tektosilicate without zeolitic H2O (09.F)
Family: without additional non-tetrahedral anions, (Al,B):Si = 1:1 (09.FA)
Code: 09.FA.35

Dana

Major class: silicates (VIII)
Class: tectosilicate Al-Si framework (76)
Type: with Al-Si frameworks (76.01)
Group: Plagioclase series (76.01.03)

Endmembers and polymorphs

End-members

Members

Albite (Na (Ab) = 90-100% - Ca = 0-10% - K (Or) = 0-10% (triclinic))
Oligoclase (Na (Ab) = 70-90% - Ca = 10-30% - K (Or) = 0-10% (triclinic))
Andesine (Na (Ab) = 50-70% - Ca = 30-50% - K (Or) = 0-10% (triclinic))
Labradorite (Na (Ab) = 30-50% - Ca = 50-70% - K (Or) = 0-10% (triclinic))
Bytownite (Na (Ab) = 10-30% - Ca = 80-90% - K (Or) = 0-10% (triclinic))
Anorthite (Na (Ab) = 0-10% - Ca (An) = 90-100% - K (Or) = 0-10% (triclinic))

Crystallography

Phase type: crystalline
Crystal system: triclinic
Crystal class: pinacoidal
Crystal class symbol: -1 (Ci)
Crystal spacegroup: P-1

Physical properties

Molar mass: 263.02 - 277.41 $g/mol$
Density: 2.61 - 2.76 $g/cm^3$

Thermodynamical properties

State NTP: solid

Optical properties

Refringence type: biaxial
Refringence sign: positive or negative
Birefringence: 0.009 - 0.012
Refraction index $n_{\alpha}$: 1.528 - 1.576
Refraction index $n_{\beta}$: 1.532 - 1.583
Refraction index $n_{\gamma}$: 1.538 - 1.588
Dispersion V: weak to relatively weak
Pure color: white
Color: white, gray, bluish white, reddish white, greenish white
Diaphaneity: transparent to subtranslucent
Luster: vitreous

Links and Publications

Links