Class

silicate mineral

Compound type

tektosilicate

Comments

Plagioclase is a wider series $(Na,Ca)(Si,Al)_4O_8$ of the feldspar group

Composition comments

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

Oxides

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

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)

Phase type

crystalline

Crystal system

triclinic

Crystal class

pinacoidal

Crystal class symbol

-1 (Ci)

Crystal spacegroup

P-1

Molar mass

263.02 - 277.41 $g/mol$

Density

2.61 - 2.76 $g/cm^3$

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

Color

white, gray, bluish white, reddish white, greenish white

Diaphaneity

transparent to subtranslucent

Luster

vitreous