Class

silicate mineral

Compound type

tektosilicate

Comments

K-feldspar (orthoclase) with Carlsbad twinning. Content = 12.93% (Hyperspectral cube classification maps).
Dimorphous with Microcline

	Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$K$	Potassium	element	1		constituent element	main
	$Al$	Aluminium	element	1		constituent element	main
	$Si$	Silicon	element	3		constituent element	main
	$O$	Oxygen	element	8		constituent element	main

Composition comments

Common replacements: Na, Ba, Ca - Common impurities: Fe, Rb

Oxides

Formula	$SiO_{2}$	$Al_{2}O_{3}$	$K_{2}O$	$Na_{2}O$	$CaO$	$FeO$
Mass fraction (%)	64.2	18.22	15.58	0.98	0.03	0.01

Oxides comments

Average composition of K-feldspar crystals.

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.30

Dana

Major class

silicates (VIII)

Class

tectosilicate Al-Si framework (76)

Type

with Al-Si frameworks (76.01)

Group

K (Na,Ba) feldspars (76.01.01)

Code

76.01.01.01

Phase type

crystalline

Crystal system

monoclinic

Crystal class

prismatic

Crystal class symbol

2/m (C2h)

Crystal spacegroup

C2/m

Molar mass

278.33 $g/mol$

Density

2.56 $g/cm^3$

Refringence type

biaxial

Refringence sign

negative

Birefringence

0.0050 - 0.0060

Refraction index $n_{\alpha}$

1.518

Refraction index $n_{\beta}$

1.522

Refraction index $n_{\gamma}$

1.523 - 1.524

Dispersion V

relatively strong

Color

colorless, greenish, grayish yellow, white, pink

Diaphaneity

transparent to translucent

Luster

vitreous