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Augite

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Formula:
(CaxMgyFez)(Mgy1Fez1)Si2O6
Where 0.4 ≤ x ≤ 0.9, x+y+z=1 and y1+z1=1

This formula is based on the definition by Morimoto et al. (1988)
Colour:
Brown-green, black, green-black, brown, purplish brown
Lustre:
Vitreous, Resinous, Dull
Hardness:
5½ - 6
Specific Gravity:
3.19 - 3.56
Crystal System:
Monoclinic
Name:
Named by Abraham G. Werner in 1792 from the Greek αυγή ("auge") for "shine" or "luster," in allusion to the appearance of its cleavage surfaces.
Pyroxene Group, Clinopyroxene Subgroup. In the Ca-Fe-Mg (diopside-hedenbergite-augite) quadrilateral, the ideal structural formula is M2M1[Si2O6], where M2 is a distorted octahedral site which preferentially accepts large cations such as alkaline earth/alkali atoms (Ca, but may accept transition metals) and where M1 is a smaller regular octahedral site preferentially accepting transition metals, etc. (most commonly Mg, Fe2+). The substitutions containing no changes in valence within M2 (2+), Mi (2+), and tetrahedral sites, T (4+), is the normal scheme. A variety of additional substitution schemes, which require coupling of substituents, have been identified in these pyroxenes. Often these substitutions result in a change of species designation when they are dominant.

Substitution 1 has Na substitution in M2 and trivalent ions of Al, Fe, Cr, and Sc substituting in M1.

Substitution 2 involves Na substitution in M2 and mixed valance transition metals such as [Fe2+0.5Ti4+0.5] substituting in M1.

Substitution 3, also called Tschermak's Component, involves coupled M1 octahedral and tetrahedral substitutions, such as CaAl[AlSiO6] or CaTi3+[AlSiO6].

Substitution 4 is a variant of Substitution 2 and has dominant Ca in M2 with mixed valence substitution in M1 involving divalent and tetravalent Ti and Al substitution in tetrahedral sites (e.g. Ca[(Mg, Fe2+ · 5Ti4+ · 5)] [AlSiO6]. In highly substituted Ca-Fe-Mg pyroxenes, several substitutional schemes may be identified.

Substitution schemes 2 and 4 have not yet yielded named mineral species.

Augite could be considered to be a sub-calcic member of the diopside-hedenbergite series but, as defined by Morimoto et al. (1988) may have Fe>Mg or Mg>Fe without a change in name. Because of the way augite has been defined (Morimoto et al, 1988), there is the implication that in rare cases, a variety of anions may be dominant in various the various sites, including M2, M1, and T. These extreme compositions are rare in the large majority of augites. The clinopyroxenes with Wo5-20 are classed as pigeonite, another mineral that could be thought of as slightly alkalic clinoenstatite-clinoferrosilite.

However, there is a structural discontinuity between these pyroxenes at low-medium temperatures, and detailed chemical analysis and even structural analysis should be obtained in order to properly classify these unusual compositions. Similarly, extensive substitution of Na, for example, as in scheme 1 (Morimoto et al., 1988) could lead to Aegirine-augite or aegirine compositions depending on the other elements involved.

Visit gemdat.org for gemological information about Augite.


Classification of Augite

Augite and its relation to other pyroxenes (after Morimoto et al, 1989)

Previous petrological nomenclature of clinopyroxenes from basaltic magmas (after Poldervaart & Hess, 1951)

Approved, 'Grandfathered' (first described prior to 1959)
9.DA.15

9 : SILICATES (Germanates)
D : Inosilicates
A : Inosilicates with 2-periodic single chains, Si2O6; pyroxene family
65.1.3a.3

65 : INOSILICATES Single-Width,Unbranched Chains,(W=1)
1 : Single-Width Unbranched Chains, W=1 with chains P=2
16.23.1

16 : Silicates Containing Aluminum and other Metals
23 : Aluminosilicates of Fe, Ca, and Mg

Physical Properties of Augite

Vitreous, Resinous, Dull
Transparency:
Translucent, Opaque
Colour:
Brown-green, black, green-black, brown, purplish brown
Streak:
Greenish gray, light to dark brown
Hardness:
5½ - 6 on Mohs scale
Tenacity:
Brittle
Cleavage:
Distinct/Good
Good on {110}
Parting:
on {100} and {010}
Fracture:
Irregular/Uneven, Sub-Conchoidal
Density:
3.19 - 3.56 g/cm3 (Measured)    3.31 g/cm3 (Calculated)

Optical Data of Augite

Type:
Biaxial (+)
RI values:
nα = 1.680 - 1.735 nβ = 1.684 - 1.741 nγ = 1.706 - 1.774
2V:
Measured: 40° to 52°, Calculated: 48° to 68°
Birefringence:
0.032
Max Birefringence:
δ = 0.026 - 0.039
Image shows birefringence interference colour range (at 30µm thickness)
and does not take into account mineral colouration.
Surface Relief:
High
Dispersion:
r > v weak to distinct
Optical Extinction:
Z : c = 35°-48°
Pleochroism:
Visible
Comments:
X= pale green, pale brown, green, greenish yellow
Y= pale brown, pale yellow-green, violet
Z= pale green, grayish green, violet

Chemical Properties of Augite

Formula:
(CaxMgyFez)(Mgy1Fez1)Si2O6

Where 0.4 ≤ x ≤ 0.9, x+y+z=1 and y1+z1=1

This formula is based on the definition by Morimoto et al. (1988)
IMA Formula:
(Ca,Mg,Fe)2Si2O6
Common Impurities:
Ti,Cr,Na,Mn,K

Crystallography of Augite

Crystal System:
Monoclinic
Class (H-M):
2/m - Prismatic
Space Group:
B2/b
Setting:
C2/c
Cell Parameters:
a = 9.699 Å, b = 8.844 Å, c = 5.272 Å
β = 106.97°
Ratio:
a:b:c = 1.097 : 1 : 0.596
Unit Cell V:
432.53 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Stubby prismatic crystals
Twinning:
Simple or multiple on {100}, also on {001}
Comment:
Axial setting is C1 2/c 1

Crystallographic forms of Augite

Crystal Atlas:
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Augite no.24 - Goldschmidt (1913-1926)
Augite no.111 - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by www.smorf.nl.

Toggle
Edge Lines | Miller Indicies | Axes

Transparency
Opaque | Translucent | Transparent

View
Along a-axis | Along b-axis | Along c-axis | Start rotation | Stop rotation

X-Ray Powder Diffraction

Powder Diffraction Data:
d-spacingIntensity
3.22 (70)
2.99 (100)
2.94 (60)
2.90 (30)
2.56 (40)
2.53 (30)
2.51 (50)
2.13 (30)
Comments:
ICDD 41-1483 (titanian augite)

Synonyms of Augite

Other Language Names for Augite

Basque:Augita
Catalan:Augita
Croatian:Augit
Czech:Augit
Dutch:Augiet
Esperanto:Aŭgito
Finnish:Augiitti
French:Augite
Hebrew:אוגיט
Hungarian:Augit
Italian:Augite
Japanese:普通輝石
Lithuanian:Augitas
Polish:Augit
Russian:Авгит
Serbian (Cyrillic Script):Аугит
Simplified Chinese:普通辉石
Swedish:Augit
Tajik (Cyrillic Script):Авгит
Ukrainian:Авгіт

Varieties of Augite

Asteroite

A stellate radiating iron-rich variety of Augite.

Originally described from Nordmark, Filipstad, Värmland, Sweden.

Fassaite

Augite with a low iron content.
Originally reported from Fassa Valley, Trento Province, Trentino-Alto Adige, Italy.

Ferroaugite

An obsolete term for a pyroxene that would now be categorized as augite.

Ferrohedenbergite

Previously defined as a clinopyroxene with Ca: 25-45% and Mg
This composition would now be classified as augite.

Korea-Augite

Distinguised by its optical properties, from an Alkali-trachyte in Korea.

Soda-Augite

Intermediate between Augite and Aegirine-Augite, unsure how this differs from the latter.

Titanian Augite

A Ti-rich variety of Augite

Relationship of Augite to other Species

Other Members of this group:
AegirineNaFe3+Si2O6
Aegirine-augite(NaaCabFe2+cMgd)(Fe3+eAlfFe2+gMgh)Si2O6
ClinoenstatiteMgSiO3
ClinoferrosiliteFe2+SiO3
DiopsideCaMgSi2O6
EsseneiteCaFe3+[AlSiO6]
HedenbergiteCaFe2+Si2O6
JadeiteNa(Al,Fe3+)Si2O6
Jervisite(Na,Ca,Fe2+)(Sc,Mg,Fe2+)Si2O6
JohannseniteCaMn2+Si2O6
KanoiteMn2+(Mg,Mn2+)Si2O6
KosmochlorNaCrSi2O6
KushiroiteCaAl[AlSiO6]
NamansiliteNaMn3+Si2O6
NatalyiteNaV3+Si2O6
Omphacite(NaaCabFe2+cMgd)(AleFe3+fFe2+gMgh)Si2O6
PetedunniteCa(Zn,Mn2+,Mg,Fe2+)Si2O6
Pigeonite(CaxMgyFez)(Mgy1Fez1)Si2O6
SpodumeneLiAlSi2O6

Common Associates

Associated Minerals Based on Photo Data:
Calcite56 photos of Augite associated with Calcite on mindat.org.
Prehnite26 photos of Augite associated with Prehnite on mindat.org.
Epidote24 photos of Augite associated with Epidote on mindat.org.
Scapolite24 photos of Augite associated with Scapolite on mindat.org.
Fluorapatite21 photos of Augite associated with Fluorapatite on mindat.org.
Scapolite Group21 photos of Augite associated with Scapolite Group on mindat.org.
Leucite18 photos of Augite associated with Leucite on mindat.org.
Ilmenite18 photos of Augite associated with Ilmenite on mindat.org.
Apatite15 photos of Augite associated with Apatite on mindat.org.
Titanite15 photos of Augite associated with Titanite on mindat.org.

Related Minerals - Nickel-Strunz Grouping

9.DA.05Donpeacorite(Mn2+,Mg)Mg[SiO3]2
9.DA.05EnstatiteMgSiO3
9.DA.05FerrosiliteFeSiO3
9.DA.10ClinoenstatiteMgSiO3
9.DA.10ClinoferrosiliteFe2+SiO3
9.DA.10KanoiteMn2+(Mg,Mn2+)Si2O6
9.DA.10Pigeonite(CaxMgyFez)(Mgy1Fez1)Si2O6
9.DA.15DiopsideCaMgSi2O6
9.DA.15EsseneiteCaFe3+[AlSiO6]
9.DA.15HedenbergiteCaFe2+Si2O6
9.DA.15JohannseniteCaMn2+Si2O6
9.DA.15PetedunniteCa(Zn,Mn2+,Mg,Fe2+)Si2O6
9.DA.15DavisiteCaScAlSiO6
9.DA.15KushiroiteCaAl[AlSiO6]
9.DA.15GrossmaniteCaTi3+ AlSiO6
9.DA.20Aegirine-augite(NaaCabFe2+cMgd)(Fe3+eAlfFe2+gMgh)Si2O6
9.DA.20Omphacite(NaaCabFe2+cMgd)(AleFe3+fFe2+gMgh)Si2O6
9.DA.25AegirineNaFe3+Si2O6
9.DA.25JadeiteNa(Al,Fe3+)Si2O6
9.DA.25Jervisite(Na,Ca,Fe2+)(Sc,Mg,Fe2+)Si2O6
9.DA.25KosmochlorNaCrSi2O6
9.DA.25NamansiliteNaMn3+Si2O6
9.DA.25NatalyiteNaV3+Si2O6
9.DA.30SpodumeneLiAlSi2O6

Related Minerals - Hey's Chemical Index of Minerals Grouping

16.23.2DorriteCa4(Mg3Fe3+9)O4(Si3Al8Fe3+O36)
16.23.3Vesuvianite(Ca,Na,☐)19(Al,Mg,Fe3+)13(☐,B,Al,Fe3+)5(Si2O7)4(SiO4)10(OH,F,O)10
16.23.5Ferro-hornblende☐{Ca2}{Fe2+4Al}(AlSi7O22)(OH)2
16.23.6Magnesio-hornblende☐{Ca2}{Mg4Al}(AlSi7O22)(OH)2
16.23.7Aerinite(Ca5.1Na0.5)(Fe3+,Al,Fe2+,Mg)4(Al,Mg)6[HSi12O36(OH)12][(CO3)1.2(H2O)12]

Related Minerals - Dana Grouping (8th Ed.)

65.1.3a.1DiopsideCaMgSi2O6
65.1.3a.2HedenbergiteCaFe2+Si2O6
65.1.3a.4JohannseniteCaMn2+Si2O6
65.1.3a.5PetedunniteCa(Zn,Mn2+,Mg,Fe2+)Si2O6
65.1.3a.6EsseneiteCaFe3+[AlSiO6]

Fluorescence of Augite

Not fluorescent

Other Information

Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.

Augite in petrology

An essential component of (items highlighted in red)
Common component of (items highlighted in red)

References for Augite

Reference List:
Sort by Year (asc) | by Year (desc) | by Author (A-Z) | by Author (Z-A)
Dana, E.S. (1892) Dana's System of Mineralogy, 6th edition, New York, NY: 352-364.
Poldervaart, A , Hess, H.H. (1951) , "Pyroxenes in the Crystallization of Basaltic Magma," The Journal of Geology 59, no. 5 (Sep., 1951): 472-489.
Clark, J.R., Appleman, D.E., Papike, J.J. (1969) Crystal-chemical characterization of clinopyroxenes based on eight new structure refinements. MSA Special Paper 2: 31-50.
Robinson, P., Ross, M., Nord, G.L., Smyth, J.R., Jaffe, H.W. (1977) Exsolution lamellae in augite and pigeonite: fossil indicators of lattice parameters at high temperature and pressure. American Mineralogist: 62: 857-873.
Phillips, W.R., Griffin, D.T. (1981) Optical Mineralogy: 196-198.
Morimoto, N., Fabries, J., Ferguson, A. K., Ginzburg, I. V., Ross, M., Seifert, F. A., Zussman, J., Aoki, K., Gottardi, G. (1988) Nomenclature of Pyroxenes. American Mineralogist: 73: 1123-1133.
Deer, W.A., Howie, R.A., Zussman, J. (1997) Rock-Forming Minerals. Volume 2A, Geological Society of London, 764pp., 294-398.

Internet Links for Augite

mindat.org URL:
https://www.mindat.org/min-419.html
Please feel free to link to this page.

Localities for Augite

Mineral and/or Locality  
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