Euclase

Chemical formula: BeAlSiO<sub>4</sub>(OH)

Euclase is a rare beryllium aluminum silicate, prized by collectors for its beautiful, most often blue crystals and perfect cleavage.

## Characteristics Euclase is a beryllium aluminum silicate, known for its well-formed, prismatic crystals. It usually occurs as single, striated crystals along the long axis, which can be transparent to translucent. Its name refers to its characteristic, very easy cleavage, which makes it an extremely difficult mineral to work with in jewelry, but at the same time highly desired by collectors. ## Physical Properties Euclase is characterized by a significant hardness of 7.5 on the Mohs scale, which makes it resistant to scratching. It has a vitreous luster and a density in the range of 3.05-3.1 g/cm³. Its most characteristic feature is its perfect, unidirectional cleavage, which causes the mineral to easily break along one plane, creating smooth surfaces. ## Colors and Varieties The most common and most valued color of euclase is blue, ranging from pale blue to a deep, sapphire hue. It also occurs in colorless, white, greenish, and more rarely, violet variants. Some crystals may exhibit color zoning, where different shades occur within a single specimen. There are no named commercial varieties, and classification is based primarily on color and origin. ## History and Name The name "euclase" comes from the Greek words *eu* (well) and *klasis* (to break), which is a direct reference to its perfect cleavage. The mineral was first scientifically described in 1792 by the French mineralogist René Just Haüy. ## Uses Due to its rarity and difficulty in processing (resulting from cleavage), euclase is almost exclusively a collector's stone. Faceted specimens are rare and highly valued, posing a challenge even for experienced lapidaries. It has no industrial applications.

Properties

Mohs hardness
7.5
Luster
Vitreous
Streak
White
Density
3.05-3.1
Cleavage
Perfect on {010}
Fracture
Conchoidal
Transparency
Transparent to translucent
Crystal system
Monoclinic

Diagnostic features

## Identification The key diagnostic feature of euclase is its perfect cleavage in one direction, often visible as perfectly flat fractures or parting surfaces. Other helpful identification features include high hardness (7.5), vitreous luster, and the characteristic prismatic habit of crystals, often with longitudinal striations. ## Distinguishing from Similar Minerals Euclase is sometimes confused with aquamarine, topaz, or sapphire. It is distinguished from aquamarine (which is also a beryllium silicate) by its higher density and perfect cleavage (aquamarine has indistinct cleavage). Topaz has similar hardness but different cleavage (perfect basal) and often a different crystal habit. Sapphire is much harder (9 on the Mohs scale) and does not exhibit cleavage. ## Crystal Forms Euclase crystallizes in the monoclinic system, forming elongated, prismatic crystals. They are often terminated by oblique faces and exhibit distinct striations on the prismatic faces, parallel to the crystallographic c-axis.

Geological environment

## Genesis Euclase is a hydrothermal mineral, crystallizing in the late stages from beryllium-rich solutions. It is most commonly found in granitic pegmatites and in Alpine-type veins, where it forms at low temperatures. It also occurs as a secondary mineral in alluvial (detrital) deposits due to its hardness and resistance to weathering. ## Mineral Associations This mineral often co-occurs with other pegmatitic and hydrothermal minerals, such as quartz, feldspars (especially albite), micas (muscovite), topaz, beryl (including aquamarine), chrysoberyl, fluorite, and apatite. ## Localities The most famous and highly prized euclase specimens come from Colombia, from the Gachalá mine, where they occur in calcite veins cutting black shales. Beautiful blue crystals are also known from Ouro Preto in Minas Gerais, Brazil. Other significant localities include Zimbabwe (Karoi area), Russia (Southern Urals), Austria (Rauris valley in the Alps), and Germany (Bavaria).

Rarity

Rare

For collectors

## Quality Criteria The most highly valued euclase specimens are those with an intense, evenly distributed blue color, high transparency, and no visible inclusions. The size and completeness of the crystal are also important – large, undamaged prisms with well-preserved terminations command the highest prices. Specimens on matrix, especially in association with other minerals, are also highly sought after. ## Market Prices Euclase prices are high due to its rarity. Small, faceted stones weighing less than 1 carat can cost from several hundred to over a thousand dollars, depending on color quality. Prices for larger, clean stones with intense color can reach several thousand dollars per carat. High-quality crystalline specimens for collectors, especially from classic localities like Colombia, can fetch prices from several hundred to many thousands of dollars. ## Popular Localities Specimens from Gachalá, Colombia, known for their deep blue color, are considered the best in the world. A classic, historical locality is Ouro Preto, Brazil, which yields beautiful, often bicolored crystals. Specimens from Zimbabwe are also valued for their attractive blue color.

Care and storage

## Cleaning Euclase should be cleaned very carefully. The safest method is to use a soft, damp cloth or brush to remove dust. It can be rinsed in lukewarm water, but ultrasonic and steam cleaners should be avoided, as they can cause cracks along cleavage planes. ## What to Avoid The mineral is sensitive to impacts and mechanical pressure, which can easily lead to its splitting. Contact with strong acids and chemicals should be avoided. Although relatively hard, storing it with harder minerals, such as diamond or corundum, can lead to scratches. ## Storage Euclase specimens are best stored separately, in padded display boxes, to protect them from impacts and contact with other minerals. Due to its fragility, it is not recommended for setting in everyday jewelry.

External references

Sources

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