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Forsterite

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Formula:
Mg2SiO4
System:
Orthorhombic
Colour:
Green, pale yellow or ...
Lustre:
Vitreous
Hardness:
7
Member of:
Name:
Known in ancient times and some smaragdus and beryllos (Pliny, 79) may have been what is now called forsterite. (N.B. The "chrysolithas" of Pliny (79) is believed to be topaz.) The earliest name given to an undisputed olivine group species was chrysolit (chrysolite) and was named by Johan Gottschalk Wallerius in 1747, although the name chrysolite was later used by Balthasar Georges Sage in 1777 for what is now known as prehnite. In 1755, Antoine Joseph Dezallier d'Argenville called this species "peridot ordinaire", while Axel Cronstedt named it "gulgron topas" in 1758. In 1772, Rome d'Lisle renamed the mineral "chrystile ordinaire". Wallerius's chrysolite was renamed, olivine, in 1789 by Abraham Gottlieb Werner for the usual olive green color of this mineral (N.B. chrysolite has a similar etymology.) Friedrich Walchner in 1823 gave it the name "hyalosiderite". Named forsterite in 1824 by Serve-Dieu Abailard "Armand" Lévy in honor of Adolarius Jacob Forster [April 6, 1739 Grossbreitenbach, Thuringia, Germany - May, 1806 St. Petersburg, Russia], English mineral collector and mineral dealer. Boltonite was introduced in 1835 by Charles Upham Shepard, while glinkit was named in 1847 by Romanovski.
Polymorph of:

Classification of Forsterite

Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
9.AC.05

9 : SILICATES (Germanates)
A : Nesosilicates
C : Nesosilicates without additional anions; cations in octahedral [6] coordination
51.3.1.2

51 : NESOSILICATES Insular SiO4 Groups Only
3 : Insular SiO4 Groups Only with all cations in octahedral [6] coordination
14.4.1

14 : Silicates not Containing Aluminum
4 : Silicates of Mg
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First Recorded Occurrence of Forsterite

Year of Discovery:
1824

Occurrences of Forsterite

Geological Setting:
In mafic and ultramafic igneous rocks, metamorphosed impure dolomites

Physical Properties of Forsterite

Vitreous
Diaphaneity (Transparency):
Transparent, Translucent
Colour:
Green, pale yellow or white.
Streak:
White
Hardness (Mohs):
7
Tenacity:
Brittle
Cleavage:
Perfect
Perfect on {010}
imperfect on {100}
Fracture:
Conchoidal
Density:
3.275 g/cm3 (Measured)    3.271 g/cm3 (Calculated)

Crystallography of Forsterite

Crystal System:
Orthorhombic
Class (H-M):
mmm (2/m 2/m 2/m) - Dipyramidal
Cell Parameters:
a = 4.754Å, b = 10.1971Å, c = 5.9806Å
Ratio:
a:b:c = 0.466 : 1 : 0.587
Unit Cell Volume:
V 289.92 ų (Calculated from Unit Cell)
Z:
4
Morphology:
Euhedral to subhedral crystals
Twinning:
{100} {011} {012}
Comment:
Data for synthetic material.

Crystal Structure

Structure
Reference
Birle J D Gibbs G V Moore P B Smith J V (1968) Crystal structures of natural olivines. American Mineralogist 53:807-824.

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More Crystal Structures
Click here to view more crystal structures at the American Mineralogist Crystal Structure Database
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.

Optical Data of Forsterite

Type:
Biaxial (+)
RI values:
nα = 1.636 - 1.730 nβ = 1.650 - 1.739 nγ = 1.669 - 1.772
2V:
Measured: 74° to 90°, Calculated: 56° to 84°
Max Birefringence:
δ = 0.033 - 0.042
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
High
Dispersion:
r > v or r < v

Chemical Properties of Forsterite

Formula:
Mg2SiO4
Essential elements:
All elements listed in formula:
Common Impurities:
Fe

Relationship of Forsterite to other Species

Series:
Forms a series with Fayalite (see here)
Forms a series with Fayalite (see here)
Forms a series with Tephroite (see here)
Member of:
Other Members of Group:
Calcio-olivineCa2SiO4
FayaliteFe22+SiO4
GlaucochroiteCaMn2+SiO4
KirschsteiniteCaFe2+SiO4
LaihuniteFe2+Fe23+(SiO4)2
Liebenbergite(Ni,Mg)2SiO4
MonticelliteCaMgSiO4
Olivine(Mg,Fe2+)2SiO4
Roepperite (of Brush)(Fe22+,Mn,Zn)SiO4
TephroiteMn22+SiO4
9.AC.05FayaliteFe22+SiO4
9.AC.05GlaucochroiteCaMn2+SiO4
9.AC.05KirschsteiniteCaFe2+SiO4
9.AC.05LaihuniteFe2+Fe23+(SiO4)2
9.AC.05Liebenbergite(Ni,Mg)2SiO4
9.AC.05TephroiteMn22+SiO4
9.AC.10MonticelliteCaMgSiO4
9.AC.15BrunogeieriteFe22+Ge4+O4
9.AC.15Ringwoodite(Mg,Fe2+)2SiO4
9.AC.20ChesnokoviteNa2[SiO2(OH)2] · 8H2O
14.4.2EnstatiteMgSiO3
14.4.3ClinoenstatiteMgSiO3
14.4.4ChrysotileMg3(Si2O5)(OH)4
14.4.5Clinochrysotile
14.4.6Orthochrysotile
14.4.7Parachrysotile
14.4.8LizarditeMg3(Si2O5)(OH)4
14.4.9TalcMg3(Si4O10)(OH)2
14.4.10SpadaiteMgSiO2(OH)2 · H2O (?)
14.4.11SepioliteMg4(Si6O15)(OH)2 · 6H2O
14.4.12LoughliniteNa2Mg3Si6O16 · 8H2O
14.4.13EifeliteKNa3Mg4Si12O30
14.4.14Stevensite(Ca,Na)xMg3-x(Si4O10)(OH)2
14.4.15AntigoriteMg3(Si2O5)(OH)4
14.4.16 Magnesio-anthophyllite

Other Names for Forsterite

Name in Other Languages:
Simplified Chinese:镁橄榄石
Traditional Chinese:鎂橄欖石

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.

References for Forsterite

Reference List:
Dana, E.S. (1892) System of Mineralogy, 6th. Edition, New York: 450-451, 451-456 (as chrysolite).

Kushiro, I. (1969), The system forsterite-diopside-silica with and without water at high pressures: American Journal of Science: 267: 269-294.

Hazen, R.M. (1976) Effects of temperature and pressure on the crystal structure of forsterite. American Mineralogist: 61: 1280-1293.

Deer, W.A., Howie, R.A., and Zussman, J. (1982) Rock-Forming Minerals. Volume 1A. Orthosilicates. Longmans, 2nd. Edition, 919 pp.: 3-336.

Francis, C.A. (1985) New data on the forsterite-tephroite series. American Mineralogist: 70: 568-575.

Zha, C.-S., Duffy, T.S., Downs, R.T., Mao, H.-K., and Hemley, R.J. (1996) Sound velocities and elasticity of single-crystal forsterite to 16 GPa. Journal of Geophysical Research: 101(B8): 17535-17545.

Brodholt, J.P. (1997), Ab initio calculations on point defects in forsterite (Mg2SiO4) and implications for diffusion and creep: American Mineralogist: 82: 1049-1053.

Brodholt, J.P. and Refson, K. (2000) An ab initio study of hydrogen in forsterite and a possible mechanism for hydrolytic weakening. Journal of Geophysical Research: 105: 18977-18982.

Internet Links for Forsterite

Specimens:
The following Forsterite specimens are currently listed for sale on minfind.com.

Localities for Forsterite

map shows a selection of localities that have latitude and longitude coordinates recorded. Click on the symbol to view information about a locality. The symbol next to localities in the list can be used to jump to that position on the map.
Mineral and/or Locality  
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