Euclase is a beryllium

Beryllium

Beryllium is the chemical element with the symbol Be and atomic number 4. It is a divalent element which occurs naturally only in combination with other elements in minerals. Notable gemstones which contain beryllium include beryl and chrysoberyl...

 aluminium

Aluminium

Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

 hydroxide

Hydroxide

Hydroxide is a diatomic anion with chemical formula OH−. It consists of an oxygen and a hydrogen atom held together by a covalent bond, and carrying a negative electric charge. It is an important but usually minor constituent of water. It functions as a base, as a ligand, a nucleophile, and a...

 silicate

Silicate minerals

The silicate minerals make up the largest and most important class of rock-forming minerals, constituting approximately 90 percent of the crust of the Earth. They are classified based on the structure of their silicate group...

 mineral (BeAlSiO₄(OH)). It crystallizes in the monoclinic crystal system

Crystal system

In crystallography, the terms crystal system, crystal family, and lattice system each refer to one of several classes of space groups, lattices, point groups, or crystals...

 and is typically massive to fibrous as well as in slender prismatic crystals. It is related to beryl

Beryl

The mineral beryl is a beryllium aluminium cyclosilicate with the chemical formula Be3Al26. The hexagonal crystals of beryl may be very small or range to several meters in size. Terminated crystals are relatively rare...

 (Be₃Al₂Si₆O₁₈) and other beryllium minerals. It is a product of the decomposition of beryl in pegmatite

Pegmatite

A pegmatite is a very crystalline, intrusive igneous rock composed of interlocking crystals usually larger than 2.5 cm in size; such rocks are referred to as pegmatitic....

s.

Euclase crystals are noted for their blue color, ranging from very pale to dark blue. The mineral may also be colorless, white, or light green. Cleavage

Cleavage (crystal)

Cleavage, in mineralogy, is the tendency of crystalline materials to split along definite crystallographic structural planes. These planes of relative weakness are a result of the regular locations of atoms and ions in the crystal, which create smooth repeating surfaces that are visible both in the...

 is perfect, parallel to the clinopinacoid, and this suggested to René Just Haüy

René Just Haüy

René Just Haüy – 3 June 1822 in Paris) was a French mineralogist, commonly styled the Abbé Haüy after he was made an honorary canon of Notre Dame. He is often referred to as the "Father of Modern Crystallography." -Biography:...

 the name euclase, from the Greek , easily, and , fracture. The ready cleavage renders the stone fragile with a tendency to chip, and thus detracts from its use for personal ornament. When cut it resembles certain kinds of beryl and topaz

Topaz

Topaz is a silicate mineral of aluminium and fluorine with the chemical formula Al2SiO42. Topaz crystallizes in the orthorhombic system and its crystals are mostly prismatic terminated by pyramidal and other faces.-Color and varieties:...

, from which it may be distinguished by its specific gravity (3.1). Its hardness (7.5) is rather less than that of topaz.

It was first reported in 1792 from the Orenburg

Orenburg

Orenburg is a city on the Ural River and the administrative center of Orenburg Oblast, Russia. It lies southeast of Moscow, very close to the border with Kazakhstan. Population: 546,987 ; 549,361 ; Highest point: 154.4 m...

 district in the southern Urals, Russia

Russia

Russia or , officially known as both Russia and the Russian Federation , is a country in northern Eurasia. It is a federal semi-presidential republic, comprising 83 federal subjects...

, where it is found with topaz and chrysoberyl

Chrysoberyl

The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula BeAl2O4. The name chrysoberyl is derived from the Greek words χρυσός chrysos and βήρυλλος beryllos, meaning "a gold-white spar". Despite the similarity of their names, chrysoberyl and beryl are two completely...

 in the gold-bearing gravels of the Sanarka. Its type locality

Type locality (geology)

Type locality , also called type area or type locale, is the where a particular rock type, stratigraphic unit, fossil or mineral species is first identified....

 is Ouro Prêto, Minas Gerais

Minas Gerais

Minas Gerais is one of the 26 states of Brazil, of which it is the second most populous, the third richest, and the fourth largest in area. Minas Gerais is the Brazilian state with the largest number of Presidents of Brazil, the current one, Dilma Rousseff, being one of them. The capital is the...

, Southeast Region, Brazil

Brazil

Brazil , officially the Federative Republic of Brazil , is the largest country in South America. It is the world's fifth largest country, both by geographical area and by population with over 192 million people...

, where it occurs with topaz. It is met with as a rarity in the mica-schist of the Rauris

Rauris

Rauris is a municipality in Salzburg in the area of Pinzgau in Austria. There are about 3,150 inhabitants living in Rauris.- Geography :...

in the Austrian Alps.