Forsterite

Big Photo

Padria, Sassari Province, Sardinia, Italy
0.28 carats
© alfredo petrov

Forsterite is named after Adolarius Jacob Forster, English mineral collector and dealer.

Forsterite is a magnesium-rich olivine mineral. It forms colourless, green, yellow, yellow green, white, transparent to translucent crystals with vitreous lustre.

Forsterite Gemstones by Colour

This table shows the variety of hues this gemstone can be found in. Click on a photo for more information.
 
 

Forsterite Gemstones by Size

This table shows distribution of Forsterite gemstone sizes that are listed on this site. This can give a good indication as to the general availability of this gemstone in different sizes.
Contributed photos
Lightest:0.28 cts
Heaviest:1.22 cts
Average:0.84 cts
Total photos:3
Do you have a larger Forsterite? Why not upload a photo?
0.28ct to 0.37ct0.37ct to 0.47ct0.47ct to 0.56ct0.56ct to 0.66ct0.66ct to 0.75ct0.75ct to 0.84ct0.84ct to 0.94ct0.94ct to 1.03ct1.03ct to 1.13ct1.13ct to 1.22ct
General Information
A variety or type of:Peridot
Chemical Formula
Mg
 
2
SiO
 
4
Michael O’Donoghue, Gems, Sixth Edition (2006)
Photos of natural/un-cut material from mindat.org
Synthetic Forsterite
Synthetic forsterite: Colour - blue; Transparent; Hardness 7; RI 1.635 - 1.670; Birefringence 0.035; Biaxial/+; SG 3.26; Pleochroism: violet - blue - purple; Orthorhombic; Inclusions: gas bubbles; Fluorescence: LW - chalky white, SW - greenish-yellow. - Gemmological Tables, Ulrich Henn and Claudio C. Milisenda, 2004, p 16

Synthetic forsterite has a strong pleochroism and can be used as a tanzanite imitation. It is grown by crystal pulling method with Cobalt added during growth to give it a blue color. - GIA, 2018
Physical Properties of Forsterite
Mohs Hardness6.5 to 7
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Specific Gravity3.23 to 3.26
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
TenacityBrittle
Anthony et al, Handbook of mineralogy (2001)
Cleavage QualityImperfect
Anthony et al, Handbook of mineralogy (2001)
FractureConchoidal
Anthony et al, Handbook of mineralogy (2001)
Optical Properties of Forsterite
Refractive Index1.635 to 1.671
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Optical CharacterBiaxial/+
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Birefringence0.034 to 0.035
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010) Doubling
Colour
Colour (General)Colorless to greenish
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
More from other references
Colour (Chelsea Filter)Neutral
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
TransparencyTransparent,Translucent
Anthony et al, Handbook of mineralogy (2001)
LustreVitreous
Anthony et al, Handbook of mineralogy (2001)
Fluorescence & other light emissions
Fluorescence (Short Wave UV)Inert to weak greenish yellow
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Fluorescence (Long-Wave UV)Inert to chalky orangy
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
Crystallography of Forsterite
Crystal SystemOrthorhombic
Herve Nicolas Lazzarelli, Blue Chart Gem Identification (2010)
HabitIn euhedral or subhedral crystals, typically thick, with wedge-shaped terminations, to 17 cm. Commonly granular or compact massive.
Anthony et al, Handbook of mineralogy (2001)
Geological Environment
Where found:In mafic and ultramafic igneous rocks and thermally metamorphosed impure
dolomitic limestones.
Anthony et al, Handbook of mineralogy (2001)
Further Information
Mineral information:Forsterite information at mindat.org
Significant Gem Localities
Myanmar
 
  • Mandalay Region (Mandalay Division)
    • Pyin-Oo-Lwin District
Norway
 
  • Møre og Romsdal
    • Vanylven
      • Almklovdalen
mindat.org
Sri Lanka
 
  • Sabaragamuwa Province
    • Ratnapura District
      • Ratnapura
Copyright © Jolyon & Katya Ralph 1993-2018. Site Map. Locality, gem & photograph data are the copyright of the individuals who submitted them. For more information please contact the . Gemdat.org is an online information resource dedicated to providing free gemmological information to all.