Euclase


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euclase

[′yü‚klās]
(mineralogy)
BeAlSiO4(OH) A brittle, pale green, blue, yellow, or violet monoclinic mineral, occurring as prismatic crystals.

Euclase

 

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.

REFERENCE

Mineralogiia gidrotermal’nykh mestorozhdenii berilliia. Moscow, 1976.

A. I. GINZBURG

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.
They had four children together (Bryce Walford McMurdo, Clarence Sinclair Darwin Bryce, Beryl May and Edith Euclase Winifred).
He himself was not at home, but his wife permitted us to see and to photograph "the most beautiful calcite in the world," a rose-shaped crystal cluster about 30 cm across, the petals wonderfully aligned and transparent along their edges, suggesting gemmy euclase crystals.
Don Gomez had taken it out of its own special showcase and now presented it proudly: a snow-white crystal cluster 30 cm across, with crystal "petals" resembling euclase crystals arrayed in a circle.
Beyer (1980) states that only a single crystal of "herderite" is known from Klein Spitzkoppe, associated with euclase.
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.
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.
There were kunzites, tanzanites, tourmalines, emeralds, even an enormous, rare and superb deep blue euclase crystal.