Augite | SSHADE

Mineral phase

IMA name: Augite

Name and identifiers

Secondary names: Volcanite

Class: silicate mineral
Compound type: inosilicate
Comments: The full Ca, ordered Orthopyroxene equivalent of Augite is the Diopside-Hedenbergite series

Chemical composition

Formula: $(Ca_x,Mg_{y1},Fe^{2+}_{y2})(Mg_y,Fe^{2+}_{1-y}).[(Si_z,Al_{1-z})O_3]_2 \ \ \ \ \$ where $x=0.5-0.9, y1,y2=0.1-0.5, y=0-1, z=0.75-1$
Chemical formula: (Ca,Mg,Fe2+)2(Si,Al)2O6
Elemental formula: (Ca)0.5-0.9 (Mg)0-1.5 (Fe2+)0-1.5 (Al)0-0.5 (Si)1.5-2 O6
Isotope mixture type: terrestrial abundance

	Formula	Name	Family	Number min-max	Isotope mole fraction	State	Relevance
	$Ca$	Calcium	element	0.5 - 0.9		constituent element	main
	$Mg$	Magnesium	element	0 - 1.5		constituent element	main
	$Fe^{2+}$	Iron(II) cation	element	0 - 1.5		constituent element	main
	$Al$	Aluminium	element	0 - 0.5		constituent element	main
	$Si$	Silicon	element	1.5 - 2		constituent element	main
	$O$	Oxygen	element	6		constituent element	main

Composition comments: relatively low in calcium with some disorder of occupancies of Fe2+ and Mg in both octahedral sites - Common substitution: Na, Al, $Fe^{3+}$ , Ti (also disordered) - Common impurities: Cr, Mn, Zn, K

Oxides composition

Oxides

Formula	$CaO$	$MgO$	$FeO$	$Al_{2}O_{3}$	$SiO_{2}$
Mass fraction (%)	23.2	16.65	6.6	9.4	44.15

Oxides comments

For

(C a_{0} .9, M g_{0.9}, F e_{0.2}^{2 +}) . (S i_{1.6}, A l_{0.4})_{2} O_{6}

$(Ca_0.9,Mg_{0.9},Fe^{2+}_{0.2}).(Si_{1.6},Al_{0.4})_2O_6$

Classifications

Strunz

Class: silicates (09)
Division: inosilicate (09.D)
Family: with 2-periodic single chains, Si2O6; pyroxene family (09.DA)
Code: 09.DA.15

Dana

Major class: silicates (VIII)
Class: inosilicate single-width unbranched chains, w=1 (65)
Type: with chains P=2 (65.01)
Group: C2/c clinopyroxenes (Ca clinopyroxenes) (65.01.03a)
Code: 65.01.03a.03

Crystallography

Phase type: crystalline
Crystal system: monoclinic
Crystal class: prismatic
Crystal class symbol: 2/m (C2h)
Crystal spacegroup: C2/c

Physical properties

Molar mass: 236.35 $g/mol$
Density: 3.19 - 3.56 $g/cm^3$

Thermodynamical properties

State NTP: solid

Optical properties

Refringence type: biaxial
Refringence sign: positive
Birefringence: 0.026
Refraction index $n_{\alpha}$: 1.680 - 1.735
Refraction index $n_{\beta}$: 1.684 - 1.741
Refraction index $n_{\gamma}$: 1.706 - 1.774
Dispersion V: weak to distinct (r > v)
Pure color: brown
Color: green, brown green, light brown, purplish brown, dark brown, black
Diaphaneity: translucent to opaque
Luster: vitreous

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