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Willemite

This page kindly sponsored by Mariusz Oleszczuk
William I of the Netherlands
Formula:
Zn2SiO4
System:
Trigonal
Colour:
Colorless, white, pastel ...
Hardness:
Name:
Originally named "silicious oxyde of zinc" in 1824 by Lardner Vanuxem and William Hypolitus Keating. Re-named in 1830 by Serve-Dieu Abailard "Armand" Lévy in honor of William I (Willem), King (1813-1840) of the Netherlands, wherein the type locality was located at the time.
Phenakite Group.

Crystals prismatic, both stout and slender, terminated by rhombohedra and {0001}, to 20 cm. Commonly tiny simple hexagonal prisms or radial tufts of acicular needles outside of the New Jersey occurrences. Coarse to fine granular, disseminated; in fibrous aggregates, botryoidal, and massive.

A relatively common secondary zinc silicate in many Pb-Zn or Zn deposits which contain or contained sphalerite, from which it is commonly formed upon oxidation in a siliceous environment.

Visit gemdat.org for gemological information about Willemite.

Classification of Willemite

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

9 : SILICATES (Germanates)
A : Nesosilicates
A : Nesosilicates without additional anions; cations in tetrahedral [4] coordination
Dana 7th ed.:
51.1.1.2
51.1.1.2

51 : NESOSILICATES Insular SiO4 Groups Only
1 : Insular SiO4 Groups Only with cations in [4] coordination
14.7.11

14 : Silicates not Containing Aluminum
7 : Silicates of Ba, Sr and Zn
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http://www.mindat.org/min-4292.html
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Type Occurrence of Willemite

Year of Discovery:
1830
Associated Minerals at Type Locality:

Occurrences of Willemite

Geological Setting:
Occurs generally as a secondary zinc mineral derived from the supergene weathering of sphalerite (gossan & other oxidized deposits) or by the alteration of primary sphalerite in hydrothermal veins. The Franklin-Sterling Hill orebodies are unique in the context of massive willemite as a primary ore mineral, derived from an unknown proto-ore during Cambrian, or older, times.

Physical Properties of Willemite

Vitreous, Resinous
Diaphaneity (Transparency):
Transparent, Translucent
Colour:
Colorless, white, pastel green, apple-green, light blue, azure-blue, yellow, burgundy-red, brown, mahogany-brown, gray, black, pink
Streak:
White
Hardness (Mohs):
Hardness Data:
Measured
Tenacity:
Brittle
Cleavage:
Distinct/Good
Good to poor {1120}, poor {0001}
Fracture:
Irregular/Uneven, Sub-Conchoidal
Density:
3.89 - 4.19 g/cm3 (Measured)    4.224 g/cm3 (Calculated)

Crystallography of Willemite

Crystal System:
Trigonal
Class (H-M):
3 - Rhombohedral
Space Group:
R3
Cell Parameters:
a = 13.93Å, c = 9.31Å
Ratio:
a:c = 1 : 0.668
Unit Cell Volume:
V 1,564.53 ų (Calculated from Unit Cell)
Z:
18
Morphology:
Blocky, hexagonal, barrel-shaped crystals, often with rounded terminations (Franklin area); commonly acicular in clusters to radial-fibrous aggregates; long-prismatic, hexagonal, doubly-terminated crystals; layered, botryoidal masses (Putta).

Crystallographic forms of Willemite

Crystal Atlas:
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Willemite no.11 - Goldschmidt (1913-1926)
3d models and HTML5 code kindly provided by www.smorf.nl.

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Edge Lines | Miller Indicies | Axes

Transparency
Opaque | Translucent | Transparent

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Along a-axis | Along b-axis | Along c-axis | Start rotation | Stop rotation
X-Ray Powder Diffraction:
Image Loading

Radiation - Copper Kα
Data Set:
Data courtesy of RRUFF project at University of Arizona, used with permission.
X-Ray Powder Diffraction Data:
d-spacingIntensity
4.10(20)
4.02(30)
3.49(70)
2.84(100)
2.63(90)
2.32(50)
1.860(40)
1.552(20)

Optical Data of Willemite

Type:
Uniaxial (+)
RI values:
nω = 1.691 - 1.694 nε = 1.719 - 1.725
Max Birefringence:
δ = 0.028
Image shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:
High

Chemical Properties of Willemite

Formula:
Zn2SiO4
Essential elements:
All elements listed in formula:
Analytical Data:
From Franklin, NJ
Gelatinizes with acids
SiO2 (26.55), (26.56)
Al2O3 (1.00), 0
Fe2O3 0, (0.23)
Fe0 (0.08), (0.81)
MnO (0.12), (8.96)
ZnO (72.11), (61.38)
PbO (0, (0.005)
MgO (0.13), (1.05)
CaO 0, (0.75)
Common Impurities:
Al,Fe,Mn,Pb,Mg,Ca

Relationship of Willemite to other Species

Structurally related to group(s):
14.7.1SanborniteBa2(Si4O10)
14.7.2KrauskopfiteBaSi2O5 · 3H2O
14.7.3WalstromiteBaCa2(Si3O9)
14.7.4MacdonalditeBaCa4Si16O36(OH)2 · 10H2O
14.7.5EricssoniteBaMn22+Fe3+(Si2O7)O(OH)
14.7.6Ericssonite-2OBaMn22+Fe3+(Si2O7)O(OH)
14.7.7GillespiteBaFe2+[Si4O10]
14.7.8AndrémeyeriteBaFe22+(Si2O7)
14.7.9PellyiteBa2Ca(Fe,Mg)2Si6O17
14.7.10TaikaniteSr3BaMn22+(Si4O12)O2
14.7.12HemimorphiteZn4Si2O7(OH)2 · H2O
14.7.13ZincsiliteZn3(Si4O10)(OH)2 · 4H2O
14.7.14HardystoniteCa2Zn(Si2O7)
14.7.15PetedunniteCa(Zn,Mn2+,Mg,Fe2+)Si2O6
14.7.16ClinohedriteCaZn(SiO4) · H2O
14.7.17JunitoiteCaZn2Si2O7 · H2O
14.7.18LarsenitePbZnSiO4
14.7.19EsperitePbCa2Zn3(SiO4)3
14.7.20HodgkinsoniteMn2+Zn2(SiO4)(OH)2
14.7.21GerstmanniteMnMgZn(SiO4)(OH)2
14.7.22GageiteMn21(Si4O12)2O3(OH)20
14.7.23FranklinfurnaceiteCa2Fe3+Mn32+Mn3+(Zn2Si2O10)(OH)8

Other Names for Willemite

Name in Other Languages:
Dutch:Willemiet
French:Willemite
Italian:Willemite
Lithuanian:Vilemitas
Polish:Willemit
Simplified Chinese:硅锌矿

Other Information

Bright green (SW UV & X-ray), often with very strong green phosphorescence; green (LW SW); Creamy-white to pastle yellow (SW & LW UV)(common).
Thermal Behaviour:
Fusibility 3-4
Health Risks:
No information on health risks for this material has been entered into the database. You should always treat mineral specimens with care.
Industrial Uses:
Ore of zinc / zinc oxide

References for Willemite

Reference List:
Vanuxem, Lardner and Keating, William Hypolitus (1824) "silicious oxyde of zinc", Journal of the Academy of Natural Science of Philadelphia, v. 4, p. 8.
Braun, M., (1857): Über die Galmeilagerstätte des Altenberges im Zusammenhang mit den Erzlagerstätten des Altenberger Grubenfeldes un der Umgegend, Zeitschrift d. Dt. Geolog. Gesellschaft

Brown, J.S. (1936) Supergene sphalerite, galena, and willemite at Balmat, NY. Economic Geology: 31: 331-354.

Mineralogical Magazine (1977): 41: 71-75.

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

Brugger, et al. (2003). Formation of willemite in hydrothermal environments: Economic Geology, v.98, pg 819-835.

Internet Links for Willemite

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

Localities for Willemite

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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