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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 {11_20}, 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

Related to:
  • 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
    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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  • Raman and XRD data at RRUFF project
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  • Search for Willemite in the Natural History Museum (London) online catalogue
  • Willemite details from Handbook of Mineralogy (PDF)
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    Localities for Willemite

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