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Willemite

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Trotter Mine (Lehigh Mine), Franklin, Franklin Mining District, Sussex Co., New Jersey, USA
© 2001 John H. Betts

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Formula:
Zn
 
2
[SiO
 
4
]
System:TrigonalColour:Colorless, white, pastel ...
Hardness:5½
Name:
Named in honour 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.

Classification of Willemite

IMA status:Valid - first described prior to 1959 (pre-IMA) - "Grandfathered"
Strunz 8th edition ID:8/A.01-20
Nickel-Strunz 10th (pending) edition ID:9.AA.05

9 : SILICATES (Germanates)
A : Nesosilicates
A : Nesosilicates without additional anions; cations in tetrahedral [4] coordination
Dana 7th edition ID:51.1.1.2
Dana 8th edition ID:51.1.1.2

51 : NESOSILICATES Insular SiO4 Groups Only
1 : Insular SiO4 Groups Only with cations in [4] coordination
Hey's CIM Ref.:14.7.11

14 : Silicates not Containing Aluminum
7 : Silicates of Ba, Sr and Zn
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Type Occurrence of Willemite

Type Locality:Vieille Montagne (Altenberg; Kelmisberg), Moresnet, Kelmis, Plombières-Vieille Montagne (Plombières-Altenberg) District, Verviers, Liège Province, Belgium
Year of Discovery:1830
Associated Minerals at type locality:
Hemimorphite

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

Lustre: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):5½
Hardness Data:Measured
Tenacity:Brittle
Cleavage:Distinct/Good
Good to poor {1120}, poor {0001}
Fracture:Irregular/Uneven, Sub-Conchoidal
Density (measured):3.89 - 4.19 g/cm3
Density (calculated):4.224 g/cm3

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).
Crystal Atlas:
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Willemite no.11 - Goldschmidt (1913-1926)

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

Optical Data of Willemite

Type:Uniaxial (+)
RI values: nω = 1.691 - 1.694 nε = 1.719 - 1.725
Maximum Birefringence:δ = 0.028

Chart shows birefringence interference colour range (at 30µm thickness) and does not take into account mineral colouration.
Surface Relief:High

Chemical Properties of Willemite

Formula:
Zn
 
2
[SiO
 
4
]
Essential elements:O, Si, Zn
All elements listed in formula:O, Si, Zn
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

Member of Group:
Phenakite Group:
Common Associates:
WulfeniteQuartzLimoniteHopeiteHemimorphite
FluoriteCalcite
Related Minerals - Nickel-Strunz Grouping):

- +
9.AA.05Eucryptite
LiAl[SiO
 
4
]
9.AA.05Phenakite
Be
 
2
[SiO
 
4
]
9.AA.10Liberite
Li
 
2
Be[SiO
 
4
]
Related Minerals - Hey's Index Grouping:

- +
14.7.1Sanbornite
Ba
 
2
[Si
 
4
O
 
10
]
14.7.2Krauskopfite
BaSi
 
2
O
 
5
·3H
 
2
O
14.7.3Walstromite
BaCa
 
2
[Si
 
3
O
 
9
]
14.7.4Macdonaldite
BaCa
 
4
Si
 
16
O
 
36
(OH)
 
2
·10H
 
2
O
14.7.5Ericssonite
BaMn
2+
2
Fe
3+
 
[O|OH|Si
 
2
O
 
7
]
14.7.6Orthoericssonite
BaMn
2+
2
Fe
3+
 
[O|OH|Si
 
2
O
 
7
]
14.7.7Gillespite
BaFe
2+
 
[Si
 
4
O
 
10
]
14.7.8Andrémeyerite
BaFe
2+
2
[Si
 
2
O
 
7
]
14.7.9Pellyite
Ba
 
2
Ca(Fe,Mg)
 
2
Si
 
6
O
 
17
14.7.10Taikanite
Sr
 
3
BaMn
2+
2
[O|Si
 
2
O
 
6
]
 
2
14.7.12Hemimorphite
Zn
 
4
[(OH)
 
2
|Si
 
2
O
 
7
] · H
 
2
O
14.7.13Zincsilite
Zn
 
3
Si
 
4
O
 
10
(OH)
 
2
·4H
 
2
O
14.7.14Hardystonite
Ca
 
2
Zn[Si
 
2
O
 
7
]
14.7.15Petedunnite
Ca(Zn,Mn
2+
 
,Mg,Fe
2+
 
)[Si
 
2
O
 
6
]
14.7.16Clinohedrite
CaZn[SiO
 
4
] · H
 
2
O
14.7.17Junitoite
CaZn
 
2
[Si
 
2
O
 
7
] · H
 
2
O
14.7.18Larsenite
PbZn[SiO
 
4
]
14.7.19Esperite
PbCa
 
3
Zn
 
4
[SiO
 
4
]
 
4
14.7.20Hodgkinsonite
Mn
2+
 
Zn
 
2
[(OH)
 
2
|SiO
 
4
]
14.7.21Gerstmannite
(Mg,Mn
2+
 
)Zn[(OH)
 
2
|SiO
 
4
]
14.7.22Gageite
Mn
 
21
O
 
3
(Si
 
4
O
 
12
)
 
2
(OH)
 
20
14.7.23Franklinfurnaceite
Ca
 
2
FeMn
 
3
MnZn
 
2
Si
 
2
O
 
10
(OH)
 
8
Related Minerals - Dana Grouping):

- +
51.1.1.1Phenakite
Be
 
2
[SiO
 
4
]
51.1.1.3Eucryptite
LiAl[SiO
 
4
]

Other Names for Willemite

Synonyms:
BelgiteHebertineVillemite
Other Languages:
Dutch:Willemiet
French:Willemite
German:Willemit
Belgit
Villemit
Italian:Willemite
Lithuanian:Vilemitas
Polish:Willemit
Russian:Виллемит
Spanish:Willemita
Belgita
Villemita
Varieties:
Beta-WillemiteGrape WillemiteRadial WillemiteSea Foam WillemiteTroostite
Xingshaoite

Other Information

Fluorescence in UV light: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
Special Storage/
Display Requirements from:
Sterling Mine,..., Sussex Co., New Jersey, USANone.
Health Warning: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: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)

Internet Links for Willemite

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    Localities for Willemite

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