Enstatite is a mineral with a hardness of 6 out of 10 on the Mohs scale of mineral hardness [?]. These Orthorhomibicly structured gems are made of magnesium iron silicate, their full chemical compound being Mg2Si2O6.
Enstatite is the most common silicate under the Orthopyroxene group in the larger classification of Pyroxene minerals (which are rock-forming silicates). Orthopyroxenes form a chemical series composed of the magnesium-rich enstatite, and the iron-containing bronzite and hypersthene.
It has an orthorhombic crystal system and appears rarely as stubby, prismatic crystals, but more commonly in fibrous or platy masses. It is hard, heavy, with good cleavage. It is very difficult to melt, and is insoluble and almost infusible. It forms a solid solution series with orthoferrosilite, originally a synthetic material discovered in lunar rocks.
Enstatite is usually light-green. It can also be brown-green, gray, or yellowish. It is transparent to opaque and has a vitreous luster, changing to pearly on cleavage surfaces, and has weak dichroism.
A rare transparent emerald-green variety occurs with diamond at Kimberley, South Africa and different colours occur in Sri Lankan alluvial deposits. A yellowish green variety has been reported from Mairimba Hill, Kenya.
It occurs in mafic and ultramafic plutonic and volcanic rocks, in high-grade metamorphic rocks (granulites), in alkalic olivine basalts, kimberlite, and meteorites (occurring as "chladnite"). It also appears as an inclusion in diamond.
Large crystals are found in the Sierra Nevada (California, USA), in Donegal (Northern Ireland), Greenland, Cima di Gagnone (Switzerland). It is common in many rocks in Scotland, Norway, Germany, South Africa (found in the blue ground with diamond), Japan, USA (Texas, Pennsylvania, Maryland, North Carolina), Finland and the Caucasus, Urals, Siberia.
Green-gray enstatite cat's eyes come from Sri Lanka, star enstatite from India, containing a six-rayed star. Further occurrences are found in South Africa and Burma.
Iron-rich enstatite is known as "elite." "Schiller spar" is a green altered enstatite, composition near to serpentine, which is also known as bastite. When the iron content of enstatite increases, then it is converted to hypersthene, and becomes opaque. Hypersthene-enstatite also exists, which is a brown intermediate stone, showing this transition.
It is usually confused with kornerupine. The metallic- green-brown variety has high iron content and is called bronzite.
"Chrome enstatite" is actually a pale to dark green variety of diopside, which contains chromium, and is not enstatite.
Its name comes from the Greek, meaning "resistor."
Enstatite is of interest to scientists and collectors. The stone is sometimes faceted, and cut cabochon, when the specimen shows chatoyancy or asterism.