ClassicGems.net

Antigorite

Discovered in 1840;   IMA status:  Valid (pre-IMA; Grandfathered)

Chemistry

Chemical Formula:

(Mg;Fe²⁺)₃Si₂O₅(OH)₄

Magnesium Iron Silicate Hydroxide

Molecular Weight:

300.77 gm

Composition:

Magnesium

18.18 %

Mg

30.15 %

MgO

Iron

13.93 %

Fe

17.92 %

FeO

Silicon

18.68 %

Si

39.95 %

SiO₂

Hydrogen

1.34 %

H

11.98 %

H₂O

Oxygen

47.88 %

O

100.00 %

100.00 %

= TOTAL OXIDE

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:

Serpentine Group (also known as Kaolinite-Serpentine Group). Polymorphous with Clinochrysotile, Lizardite, Orthochrysotile, and Parachrysotile.

Members of Group:

Serpentine Group (also known as Kaolinite-Serpentine Group): Amesite, Antigorite, Berthierine, Brindleyite, Caryopilite, Chrysotile, Clinochrysotile, Cronstedite, Dickite, Fraipontite, Greenalite, Halloysite, Kaolinite, Kellyite, Lizardite, Manandonite, Nacrite, Népouite, Odinite, Orthochrysotile, Parachrysotile, Pecoraite

Varieties:

Al-Antigorite, Andes Jade, Bowenite, Jenkinsite, Picrolite, Picrosmine, Vorhauserite, Webskyite, Williamsite

Synonyms:

Baltimorite, Bastard Asbestos, Genthite, Gymnite, Iron-Gymnite, Nickel-Gymnite, Porcellophite, Protoantigorite, Septeantigorite, Thermophyllite, 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:

Perfect on {001}, 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

Pleochroism:

None

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:

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

Year Discovered:

1840

View mineral photos:

Antigorite Mineral Photos and Locations

More Information

Mindat.org
Webmineral.com

Antigorite is a member of the Serpentine Group of minerals that also includes Chrysotile and Lizardite. The Serpentine Group is a subgroup of the Kaolinite-Serpentine Group. Most Antigorite is opaque and fibrous but a few locations produce beautiful, translucent, pale to dark green material suitable for cabochons, carvings and rarely faceted gems.

Antigorite was named in 1840 by Swiss chemist Mathias Eduard Schweizer (1818 - 1860) for the type locality, Valle di Antigorio, Domodossola, Piedmont, Italy; although there is some question whether it was found on the Italian side or the Swiss side of the border.

There are a couple of gem varieties of Antigorite; Bowenite and Williamsite. Bowenite is a translucent, light to dark green, rarely blue-green, variety. Bowenite from China is translucent and light yellowish green while Bowenite from New Zealand can be dark green. Williamsite is a translucent, pale, apple green variety that often contains inclusions of dark, octahedral microcrystals of Chromite. There is also a chromian (Cr) rich variety of Antigorite. Chromian Antigorite is colored lavender to deep purple by its chromium content. It is typically opaque, massive material that makes for very attractive mineral specimens. Faceted gems are also very attractive but rare.

Sources of Antigorite include the type locality; Antigorio Valley, Piedmont, Italy; New South Wales, Australia; Tirol Austria; Liaoning Province, China; Nagasaki and Fukuoka Prefectures, Japan; Glen Urquhart, Scotland; and in the USA at Texas, Pennsylvania; Baltimore, Maryland; and Brewster, New York. Most of these locations produce opaque, fibrous material not suitable for faceted gems or cabochons.

Antigorite gems for sale: