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Williamsite    (variety of Antigorite)
Current inventory:  0 gems
 

  
Williamsite is named named after L. W. Williams (1804-1873) who first discovered it. Antigorite is named after its discovery location of Antigorio Valley, Piedmont, Italy.

Discovered in 1840 (Antigorite);   IMA status: Williamsite is Not Valid; Antigorite is Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Mg;Fe²⁺)₃Si₂O₅(OH)₄

Magnesium Iron Silicate Hydroxide

Molecular Weight:

300.77 gm

Composition: 

Classification

Mineral Classification:

Silicates (Germanates)

Strunz 8th Ed. ID:

8/H.27-10

Nickel-Strunz 10th Ed. ID:

9.ED.15

9 : SILICATES (Germanates)
E : Phyllosilicates
D : Phyllosilicates with kaolinite layers composed of tetrahedral and octahedral nets

Related to:

Kaolinite-Serpentine Group. Polymorphous with Clinochrysotile, Lizardite, Orthochrysotile, and Parachrysotile.

Varieties:

Al-Antigorite, Andes Jade, Bowenite, Jenkinsite, Picrolite

Synonyms:

Baltimorite, Bastard Asbestos, Genthite, Gymnite, Iron-Gymnite, Nickel-Gymnite, Porcellophite, Protoantigorite, Septeantigorite, Thermophyllite, Williamsite, Yu yen shi stone, Yu yen stone, Zermattite

Crystal Data

Crystallography:

Monoclinic - Domatic

Crystal Habit:

Minute crystals, typically platy along [001], rarely elongated along [010]; some plates have rectangular outline due to cleavage; commonly bladed or fibrous.

Twinning:

May exhibit two- or three-fold twins rotated 60° about an axis [001].

Physical Properties

Cleavage:

{001} Perfect, observed on {100} and {010}

Fracture:

Conchoidal or Splintery

Tenacity:

Brittle

Moh's Hardness:

3.5 - 4.0

Density:

2.50 - 2.60 (g/cm³)

Luminescence:

None

Radioactivity:

Not Radioactive

Optical Properties

Color:

Green, Blue-Green, White; Colorless to pale Green in thin section.

Transparency:

Translucent to Sub-Opaque

Luster:

Resinous, Greasy, Silky, Waxy, Earthy

Refractive Index:

1.555 - 1.573  Biaxial ( - )

Birefringence:

0.005 - 0.006

Dispersion:

Weak; r > v

Occurances

Geological Setting:

Commonly replaces ultramafic rocks, pervasively or in crosscutting veinlets. As a replacement of siliceous dolostone along contacts with diabase sills.

Common Associations:

Chromite, Chrysotile, Magnetite, Olivine

Common Impurities:

Ni, Al, Mn

Co-Type Localities:

(Antigorite) Antigorio Valley, Ossola Valley, Verbano-Cusio-Ossola Province, Piedmont, Italy; Geisspfad area, Binn Valley, Wallis (Valais), Switzerland

Year Discovered:

1840 (Antigorite)

View mineral photos:

Antigorite Mineral Photos and Locations

More Information

Mindat.org (Antigorite)
Webmineral.com (Antigorite)

Williamsite is a translucent to nearly transparent pale apple-green variety of Antigorite. Antigorite is a member of the Serpentine Group of minerals and Williamsite is sometimes referred to as "Precious Serpentine" because it closely resembles fine Jade. It commonly contains minor inclusions of Chromite and Magnetite.

Williamsite originally came from the historic State Line Chrome Mine which lies just inside Lancaster County, Pennsylvania on the Pennsylvania-Maryland border. This mine was active from the 1800's into the early 1900's. Williamsite can occassionally be found at Wood's Chrome Mine, Texas, Little Britain Township, Lancaster County, Pennsylvania, USA.
 

  
Williamsite gems for sale:

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