Enstatite - Encyclopedia

    Class : Silicates
    Subclass : Inosilicates
    Crystal system : Orthorhombic
    Chemistry : MgSiO3
    Rarity : Common


Enstatite belongs to the group of orthorhombic pyroxenes (or orthopyroxenes). It is a constituent of basic and ultrabasic rocks (pyroxenites, peridotites and more rarely gabbros and norites), also present but rarer in high degree metamorphic rocks (granulites and charnockites), contact deposits (cornean), or volcanic rocks. Enstatite (magnesian) forms a continuous series with ferrosilite (iron), bronzite being a variety of enstatite of intermediate composition. Magnesian orthopyroxenes deteriorate into talc or serpentine, iron-bearing orthopyroxenes rather into amphibole ("uralitization"). It is a mineral that takes its name from the Greek enstatês (antagonist), alluding to its heat refractory character. Net crystals are rare and only known in gabbroic pegmatites : they are then flattened prisms. Enstatite usually occurs in fibrous, lamellar, grainy or compact masses, white, grayish to yellowish, greenish to light brown, sometimes dark green. It is exceptionally used as a gemstone when it occurs as bright green, colorless or brown crystals, with a clear asterism ; specimens with strong speckles are exploited for ornamental purposes in Canada, India and Brazil (bronzite).

84.00 ct bronzite from India

96.00 ct bronzite from India

44.55 ct bronzite from India

57.00 ct bronzite from India

Enstatite in the World

Very large crystals (up to 50 cm) come from the gabbroic pegmatites of Bamle (Norway). The United States (Tilly Foster, New York and Boulder, Colorado) as well as Brazil (Brumado, Bahia) also provided 2 cm crystals grouped in coarse or lamellar aggregates. Entatite is able to provide magnificent transparent crystals with gemmy quality such as those from Madagascar (Mount Ankaratra), Ratnapura and Elahera (Sri Lanka : colorless, green to brown gem crystals), Myanmar (Mogok), or India (crystals with strong asterism).

Enstatite in France

This mineral species is very present in millimeter crystals in the volcanic rocks of the Massif Central and more particularly of Cantal, Mont-Dore and the Chaîne des Puys.
 
Photo of enstatite gemmy crystals from Puy de Menoyre near Mauriac (Cantal) - Photo & collection Y. Vessely

Twinning

No twin known for this mineral species. On the other hand, orthopyroxenes such as enstatite may exhibit exsolutions of clinopyroxene (augite) just as augite may exhibit exsolutions of orthopyroxene. These oriented exsolutions are often confused with twinning.


On the left, a photo of an orthopyroxene exsolution in augite (yellow bands) in analyzed-polarized light.

Fakes and scams

No fake recorded for this mineral species.



Hardness : 5 to 6
Density : 3.2 to 3.9
Fracture : Irregular
Trace : White to grey




TP : Translucent to transparent
IR : 1.650 to 1.679
Biréfringence : 0.009 to 0.011
Optical character : Biaxial +
Pleochroism : Visible
Fluorescence : None


Solubility : Hydrofluoric acid

Magnetism : Paramagnetic
Radioactivity : None