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Enstatite

earth science Maturity 7-9 Next article →

Enstatite is a vital rock-forming mineral. It belongs to the pyroxene silicate group. This group includes a series of minerals that change based on their chemical makeup. Enstatite is the magnesium endmember of this series. This means it is the version that contains the most magnesium. Its chemical formula is MgSiO3. The other end of the series is ferrosilite, which is FeSiO3. Ferrosilite is rich in iron instead of magnesium.

Enstatite-83152
Enstatite-83152

Scientists study how these two minerals mix together. This mixture is called a solid solution series. The composition is often written using relative proportions. For example, En80Fs20 means the mineral is 80% enstatite and 20% ferrosilite. Historically, intermediate compositions were called hypersthene. That name has been formally replaced by the term orthopyroxene. This helps scientists be more precise when they identify minerals. Understanding these proportions helps geologists understand how rocks formed.

Enstatite can change its crystal structure. These different forms are called polymorphs. Most natural crystals are orthorhombic. This refers to their specific geometric shape. High temperature and low pressure create protoenstatite and protoferrosilite. These are also orthorhombic. However, low temperature forms change their structure. These are called clinoenstatite and clinoferrosilite. These forms are monoclinic, which is a different crystal shape.

Enstatite-83152
Enstatite-83152

Weathering can also change the appearance of the mineral. When enstatite weathers and gains a small amount of iron, it changes. It develops a submetallic luster and a bronze-like color. This material is called bronzite. Scientists now say bronzite is actually just altered enstatite. People knew about bronzite and hypersthene long before enstatite was named. The scientist G. A. Kenngott first described enstatite in 1855.

Enstatite-pas-146b
Enstatite-pas-146b

Some varieties of enstatite are used as gemstones. One variety is called chrome-enstatite. It is an emerald-green color. This color comes from small traces of chromium. Other types are used as semi-precious stones. These include black, chatoyant hypersthene and brownish bronzite. Enstatite itself can be white, gray, greenish, or brown. It has a hardness of 5–6 on the Mohs scale. Its specific gravity is 3.2–3.3.

Enstatite-83152
Enstatite-83152

Enstatite is found in many geological environments. It is an essential part of the Earth's mantle. In the mantle, it is found in rocks like peridotite and pyroxenite. It is often close to an En90Fs10 composition. It also appears in igneous rocks like gabbro and diorite. It can form small crystals in volcanic rocks like basalt, andesite, and dacite. In 1874, researchers found massive crystals in Norway. These crystals were a foot in length. They were found in apatite veins near Brevik.

Enstatite-pas-146b
Enstatite-pas-146b

This mineral is also important for studying space. Enstatite is a common mineral in meteorites. It appears in both stony and iron meteorites. One notable meteorite fell at Breitenbach in the Ore Mountains of Bohemia. In some meteorites, it forms small spherical masses called chondrules. It can also be found in the atmosphere of the young brown dwarf 2M2224-0158. There, it may exist in clouds of quartz and enstatite.

Enstatite-83152
Enstatite-83152

Beyond our Solar System, enstatite is very significant. It is one of the few silicate minerals seen in crystalline form in deep space. It is observed around evolved stars and planetary nebulae like NGC 6302. It is also a main component of E-type asteroids. The Hungaria asteroids are a major example in our Solar System. Scientists believe enstatite represents an early stage for crystalline silicates in space. Studying its chemistry helps researchers reconstruct the depths of the Earth's mantle.

Enstatite-83152
Enstatite-83152
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