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BeAlSiO4(OH) A brittle, pale green, blue, yellow, or violet monoclinic mineral, occurring as prismatic crystals.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.
The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.



a mineral of the nesosilicate subclass, with the chemical composition AlBe[SiO4](OH). Euclase contains admixtures of Ge, Mn, Cu, and, sometimes, Y, B, Sn, Zn, and Pb.

Euclase crystallizes in the monoclinic system. Its structure consists of zigzag-like chains of [BeO3(OH)] incrustated with SiO4 tetrahedrons. The latter are bound by aluminum atoms in octahedral coordination. Lamellar and short and long prismatic crystals are typical, as well as plumose and divergent aggregates, seldom larger than 1 cm across. Vertical striation is common on the facets of the prism. Euclase may be colorless, milky white, light yellow, pale blue, or greenish. It has a vitreous luster and is transparent to translucent. It typically has perfect cleavage. Its hardness on Mohs’ scale is 7.5, and its density is 3,020–3,100 kg/m3.

Euclase is usually found in hydrothermal deposits of the fluorite-phenakite-bertrandite formation, where it is associated with muscovite, quartz, fluorite, phenakite, and bertrandite or with tourmaline, fluorite, and chrysoberyl. It sometimes occurs in granitic pegmatites, where it develops together with bertrandite after beryl, and in alpine veins. Large transparent crystals of euclase are gems of order, or class, I. Euclase, together with phenakite, bertrandite, and sometimes chrysoberyl, is included in the composition of complex beryl ores.


Mineralogiia gidrotermal’nykh mestorozhdenii berilliia. Moscow, 1976.


The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.
References in periodicals archive ?
You'll be understanding if, when you obtain a copy of the book, you turn to the Santa Tereza chrysoberyl (page 106: Keith Proctor collection), Morro Velho gold (page 150: Alvaro Lucio collection), Lavra Caba Saco rutile (page 288: Luiz Menezes collection), Brumado dolomite (page 317: Julio Landmann collection), Ouro Preto crocoite (page 331: Alvaro Lucio collection), Sapo mine fluorapatite (page 347: Jim and Gail Spann collection), Malacacheta autunite (page 357: Luiz Menezes collection), or nearly any one of the stunning specimens of topaz, elbaite, beryl, euclase, etc.
Thomas Nagin of Crystal Springs Mining Company and Gallery (see above under Colombian euclase) has just begun gathering amethyst specimens at his new open-pit working in Kenya, two hours' drive east of Nairobi, called the Baobab mine, Kitui, Kitni Province.
They had four children together (Bryce Walford McMurdo, Clarence Sinclair Darwin Bryce, Beryl May and Edith Euclase Winifred).
This very interesting city hosts a mining school and possesses the best mineralogical museum in Brazil, with a special emphasis on minerals of the region (there is a special sub-collection of "imperial" topaz and euclase).
Euclase crystals up to 5 mm have been identified on one specimen from Klein Spitzkoppe (Beyer, 1980).
Also here were lovely, lustrous thumbnail-size clusters of pale to medium-pink fluorapatite crystals; a couple of superb brown parisite crystals approaching 2 cm; and wonderful pale blue, gemmy euclase crystals to a remarkable 7 cm, with sharp wedge-terminations and no side-cleavage wounds at all.
On occasion, interesting species such as euclase, apatite, topaz and kesterite with mushistonite have also been found.
Surveying this latter table, one wishes (if one is a mineral collector) that certain gem materials of "non-traditional" type, listed here, had been awarded chapters of their own: benitoite, brazilianite, euclase, sinhalite, or even sphalerite might justly have claimed more text-space (we think, if we are mineral collectors) than chalcedony or amber, each of which gets a large chapter.
Only after examination at the University of Dresden were the crystals identified as euclase. Inevitably this specimen, and perhaps others, disappeared into private hands before it could be determined whether the specimen(s) show other species which also had not yet been seen, or are very rare, at Xuebaoding.
Little Big Stone (Frederic Gautier, BP 5221, 101 Antananarivo, Madagascar) had an excellent array of crystallized specimens from this island: there was a small group of euclase specimens, mostly thumbnails, and one small miniature, marked up to [euro]170, and there was pezzottaite priced from $120-$160/gram for loose hexagonal crystals up to small miniature size.
In the booth of Tironi Minerali (via Nazionale 11/A, 23020 Prata Camportaccio So, Italy), we found a good selection of new euclase crystals from Rio Grande do Norte, Brazil--no prices were marked but the finest one was a 2.5 X 2.5-cm crystal, colorless with the typical blue stripe running down through the middle.
There were kunzites, tanzanites, tourmalines, emeralds, even an enormous, rare and superb deep blue euclase crystal.