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THE MINERAL HYPERSTHENE



Hypersthene is a relatively common mineral and is found in
igneous and some metamorphic rocks as well as in stony and iron meteorites. It forms a solid solution series with the minerals enstatite and ferrosilite . A solid solution series occurs when two or more elements can substitute for each other in a crystal structure without much alteration of the structure. In this case, the elements are iron and magnesium and enstatite is the magnesium end member of the series. Hypersthene is the intermediate member with around 50% iron and ferrosilite is the iron rich end member of the series. Enstatite is fairly common but ferrosilite is extremely rare. The iron deeply colors the minerals and therefore any deeply colored specimens of this series are usually called hypersthene. In fact the two most common members of the series are often considered together as enstatite-hypersthene in many mineral guides and texts.

Hypersthene is an orthopyroxene or a pyroxene with an orthorhombic symmetry. At high temperatures, hypersthene's structure changes to a structure with a monoclinic symmetry, a clinopyroxene or more specifically, clinohypersthene. Clinohypersthene is a polymorph of hypersthene, meaning that it has the same chemistry but a different structure.

Hypersthene has an ornamental variety. A weathered variety that has a submetallic luster and a bronze like color is called "bronzite". It is sometimes used as an ornamental stone. Both enstatite and hypersthene contribute to the bronzite variety. Some hypersthene is seen on the gemstone markets but is not well known.

The name hypersthene is from the Greek and means "over strength". It is in allusion to its greater hardness than the amphibole mineral hornblende, a mineral with which it is often confused.

PHYSICAL CHARACTERISTICS:

  • Color is gray, brown or green.
  • Luster is vitreous to pearly. Weathered specimens can have a submetallic luster ("bronzite").
  • Transparency: Crystals are generally translucent and rarely transparent.
  • Crystal System is orthorhombic; 2/m 2/m 2/m
  • Crystal Habits include rare individual crystals that have a stubby prismatic habit. More typically massive or in coarse lamellar or fibrous aggregates.
  • Cleavage is perfect in two directions at nearly 90 degrees.
  • Fracture is uneven.
  • Hardness is 5 - 6.
  • Specific Gravity is approximately 3.4 - 3.9+ (above average for non-metallic minerals)
  • Streak is white.
  • Other Characteristics: Index of refraction is approximately 1.69 - 1.77.
  • Associated Minerals include iron and stony meteorites, olivine, biotite, quartz, feldspars such as labradorite and certain types of garnets such as almandine.
  • Notable Occurrences include the North Creek, New York, USA and Labrador, Canada.
  • Best Field Indicators are color, crystal habit, hardness, cleavage, index of refraction and luster.

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