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Euclase


A rare beryllium mineral, sometimes cut as a collector’s gem


Author: , Ph.D., GIA Graduate Gemologist


Euclase

Euclase Crystal: A beautiful blue crystal of euclase with a nice termination and obvious striations. This specimen measures approximately 2.1 x 1.3 x 0.3 centimeters in size and is from Gachala, Boyaca Department, Colombia. Specimen and photo by Arkenstone / www.iRocks.com.

What Is Euclase?

Euclase is a rare beryllium aluminum hydroxide silicate mineral that crystallizes in the monoclinic system. It has a chemical composition of BeAlSiO4(OH). Euclase crystals are usually found in granitic pegmatites and low-temperature hydrothermal deposits. Massive to fibrous euclase is usually found in schists and phyllites.

It is safe to say that most geologists have never knowingly encountered euclase in the field. It is a rare mineral, they are not expecting to see it, it is usually present in small quantities, and because most euclase is colorless to white it is easily overlooked.



Physical Properties of Euclase

Chemical Classification Beryllium Silicate
Color Most euclase is colorless or white. However, its color ranges from blue to green to yellowish green. Blue euclase is a favorite of gem and mineral collectors.
Streak White or colorless (when harder than the streak plate)
Luster Vitreous
Diaphaneity Transparent to translucent
Cleavage Perfect cleavage in one direction. Cleavage faces sometimes have a pearly luster. Conchoidal fracture.
Mohs Hardness 7.5
Specific Gravity 3.0 to 3.1
Diagnostic Properties Prismatic crystals with obvious striations, perfect cleavage, color. Colored crystals are usually light in tone and may be pleochroic.
Chemical Composition BeAlSiO4(OH)
Crystal System Hexagonal
Uses No important industrial uses. High-quality crystals are prized by mineral collectors. Specimens with good color and high clarity are faceted as gems for collectors.

Euclase for Gem and Mineral Collectors

Euclase is best known for its prismatic crystals with prominent striations and a beautiful blue color with a light tone. Excellent crystal specimens are prized by mineral collectors. Specimens with excellent blue color and high clarity are often faceted into gems for mineral collectors.

Euclase has a hardness of 7.5, which would make it an excellent gem. However, it also breaks easily along planes of perfect cleavage, and that reduces its usefulness as a gem used in jewelry. The name “euclase” is derived from the Greek words eu and klasis, which together mean “good fracture”.




Geographic Occurrence

Euclase was first reported from the Orenburg district of Russia’s Ural Mountains where it occurs with other gem materials and gold in stream gravels. The most important source of gem- and specimen-quality euclase today is from Ouro Preto, in the Minas Gerais area of Brazil. Noteworthy euclase occurrences include: Australia, Austria, China, Colombia, Colorado (USA), Germany, Russia, and Zimbabwe.

Mineral collection

The best way to learn about minerals is to study with a collection of small specimens that you can handle, examine, and observe their properties. Inexpensive mineral collections are available in the Geology.com Store.



More Minerals
  Diamonds Do Not Form From Coal
  Mineral collectors
  Geodes
  The Streak Test
  Mohs Hardness Scale
  Diopside
  Quartz
  Crystal Habit

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