How do I identify Antigorite?

Antigorite can be identified by its hardness of 3.5 - 4 on the Mohs scale, green color. Look for these key characteristics when examining specimens.

What color is Antigorite?

Antigorite typically appears in green, green-blue, white, brown, black. Color can vary depending on impurities and formation conditions.

How hard is Antigorite?

Antigorite has a hardness of 3.5 - 4 on the Mohs scale. This gives it moderate hardness.

Antigorite

A variety of Minerals

What is Antigorite?

Antigorite is a lamellated, monoclinic mineral in the phylosilicate serpentine subgroup with the ideal chemical formula of (Mg,Fe)3Si2O5(OH)4. It is the high-pressure polymorph of serpentine and is commonly found in metamorphosed serpentinites. Antigorite, and its serpentine polymorphs, play an important role in subduction zone dynamics due to their relative weakness and high weight percent of water (up to 13 weight % H2O). It is named after its type locality, the Geisspfad serpentinite, Valle Antigorio in the border region of Italy/Switzerland and is commonly used as a gemstone in jewelry and carvings.

Optical Properties

Refractive Index: 1.530-1.575
Optical Character: Biaxial negative

Antigorite Market Value Calculator

Estimate the market value of Antigorite using size, quality, and finish. This preview calculator is for quick context and is not a formal appraisal.

Antigorite Localities Map

See where Antigorite is found with a localities map, collecting zones, and geology context. Generate a sample map preview below.

Map preview

North ZoneCentral RidgeSouth Basin

The Meaning

There are two varieties of antigorite, Bowenite and Williamsite. Bowenite is the state emblem of Rhode Island, and features strongly in US history, being given to Mrs. Lady Bird Johnson, the First Lady in 1967, in the form of a brooch, famously called the "Our Mineral Heritage Brooch." It was also thought to have been used in historical carvings.

Key Characteristics

Characteristics of Antigorite

Lamellated antigorite occurs in tough, pleated masses. It is usually dark green in color, but may also be yellowish, gray, brown or black. It has a Mohs scale hardness of 3.5–4 and its lustre is vitreous to greasy. Antigorite has a specific gravity of 2.5-2.6. The monoclinic crystals show micaceous cleavage, a distinguished property of phylosilicates, and fuse with difficulty. Serpentinite rocks that consist of mostly antigorite are commonly mylonites. The antigorite grains that make up these rocks are very fine (on the order of 1 to 10 microns) and are fibrous, which defines a texture in the rock caused by lattice preferred orientation.

Composition of Antigorite

The magnesian serpentines (antigorite, lizardite, chrysotile) are trioctahedral hydrous phyllosilictes. Their structure is based on 1:1 octahedral-tetrahedral layer structures. Antigorite is monoclinic in the space group Pm. Although the magensian serpentines have similar compositions, they have significantly different crystallographic structures, which are dependent on how the SiO4 tetrahedra sheets fit in with the octahedral sheets. Antigorite's basic composition has a smaller ratio of octahedral to tetrahedral cations (relative to lizardite and chrysotile), allowing the structure to compensate for the misfit of sheets through periodic flipping of the curved tetrahedra layers, and subsequently their polarity. Polysomes of antigorite are defined by the number of individual tetrahedra (denoted as the value m) which span a wavelength of the direction of curvature. The sheets of tetrahedra allow the platy, fibrous crystals to separate parallel to the 001 (basal) plane, giving antigorite its perfect cleavage.