Hypersthene

Description

Hypersthene is an orthopyroxene mineral, an intermediate member of the enstatite (MgSiO3) - ferrosilite (FeSiO3) solid solution series. Its chemical formula is (Mg,Fe)SiO3, with iron content typically ranging from 30% to 50% of the (Mg,Fe) sites. It is characterized by its dark color, often with a distinctive bronze-like metallic luster or schiller (chatoyancy) on cleavage surfaces, which is caused by minute exsolution lamellae of other minerals or inclusions. It is an important rock-forming mineral in many igneous and metamorphic rocks.

How to Identify

Color

Dark brown, greenish-black, black, grayish-brown. Often exhibits a bronze-like sheen or schiller.

Luster

Vitreous to pearly on cleavage surfaces, often with a submetallic to bronze-like schiller (chatoyancy).

Texture

Typically massive, granular, or in lamellar aggregates. Crystals are usually prismatic.

Crystal Form

Orthorhombic system, typically forming prismatic crystals, often with a rectangular cross-section. Can also be massive or lamellar.

Cleavage

Perfect cleavage in two directions at nearly 90 degrees (orthopyroxene characteristic).

Geological Environment

Mafic and ultramafic igneous rocks (norites, gabbros, pyroxenites), high-grade metamorphic rocks (granulites, charnockites), and some meteorites.

Key Facts

• Hardness: 5 - 6 on the Mohs scale
• Specific Gravity: 3.4 - 3.9 (increases with Fe content)
• Crystal System: Orthorhombic
• Color: Dark brown, greenish-black, black, grayish-brown; often with a bronze-like schiller.
• Luster: Vitreous to pearly on cleavage surfaces, submetallic to bronze-like schiller.
• Transparency: Translucent to opaque
• Fracture: Uneven to conchoidal
• Cleavage: Perfect on {210} and {100} at nearly 90 degrees.
• Composition: (Mg,Fe)SiO3 (Magnesium Iron Silicate)

Quick Check

• Color: Dark brown to black, often with a bronze sheen.
• Luster: Vitreous to pearly, with common submetallic schiller.
• Streak: Grayish-white to pale brown.

Physical Characteristics

• Crystal Habit: Prismatic, tabular, massive, lamellar, granular.
• Cleavage Type: Perfect in two directions at nearly 90 degrees (orthopyroxene cleavage).
• Fracture Type: Uneven to conchoidal.
• Tenacity: Brittle.
• Luster Type: Vitreous to pearly, often with a submetallic to bronze-like schiller.

Formation

Hypersthene forms primarily in high-temperature, high-pressure metamorphic and igneous environments. It is a common constituent of mafic and ultramafic igneous rocks (e.g., norites, gabbros, pyroxenites) and high-grade metamorphic rocks (e.g., granulites, charnockites). It can also occur in some meteorites.

Usage

Hypersthene has limited industrial uses. It is primarily of scientific interest for petrological studies, particularly in understanding the formation and evolution of mafic and ultramafic rocks and high-grade metamorphic terrains. Gem-quality specimens with strong chatoyancy or schiller effect are occasionally cut as cabochons for collectors.

Age Distribution

Found in rocks of various ages, from Precambrian to Cenozoic, depending on the geological setting.

Where to Find

Finding Tips

Similar Rocks

Scientific Classification

Mineral Class

Silicates

Group

Pyroxene Group, Orthopyroxene Subgroup

Crystal System

Orthorhombic

Chemical Formula

(Mg,Fe)SiO3

Composition

Magnesium Iron Silicate

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