Amesite - Encyclopedia

    Class : Silicates
    Subclass : Phyllosilicates
    Crystal System : Triclinic
    Chemistry : Mg2AlSiAlO5(OH)4
    Rarity : Rare

Amesite is a phyllosilicate of the serpentine group, usually pale green in color, turning pink and purplish in common chrome varieties. It owes its name to James Ames, owner of the Chester (Massachusetts) mines where it was discovered. Its crystals are pseudo-hexagonal lamellae and columnar prisms, constantly twinned, not exceeding a few millimeters. Amesite occurs mainly in foliated aggregates. It is an alteration mineral that can form in different contexts : calcium metasomatosis of granite, skarns, serpentinization of chrome dunites, etc... It is a mineral that has no particular use and remains little known to collectors.

Amesite in the World

The finest specimens of amesite are greenish gray foliated masses and 4 mm cream colored crystals from Postmasburg (South Africa). Thetford Mines, in Quebec, and the Chester Emery mine (Massachussetts, USA) also provided interesting samples. The chromiferous variety is well represented in the Russian chromite mine of Saranovsk, in the Ural Mountains where it can be associated with intense green chromiferous titanites (photo on the right).

Amesite in France

In France, chromiferous amesite is found in the serpentinites of Mouirange (New Caledonia), and in millimetric cream-colored crystals at Prudeux near St-Babel (Puy-de-Dôme) in a tephrite flow (see photo opposite by Jean-Marc Johannet).

Twinning and special crystallizations

Twins are common on {001} (star twin) and polysynthetic parallel to {010}.
At right, an enlarged Robert Meyer image of amesite star-twinned crystals from Cerro Sapo, Ayopaya Province, Cochabamba, Bolivia. Specimen donated by Alfredo Petrov to the Seattle Mineral Market. The field width is 1.8 mm.

Fakes and scams

No fake inventories for this species.

Hardness : 2.5 to 3
Density : 2.77 to 2.78
Fracture : Micaceous

Streak : White

TP : Translucent to transparent
IR : 1.596 to 1.616
Birefringence : 0.018 to 0.019
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None

Solubility : None

Magnetism : None
Radioactivity : None