Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia



EUCLASE (Euclas—Euclase—Ёвклаз) (Haüy, R.J. 1792), from Gk. “eu” – well and “klas” – a break, alluding to its perfect cleavage.

Composition & Properties. Silicate – Al[6]Be[4][OH|SiO4], subclass orthosilicates, monoclinic system. Hardness 6.5-7.5. Density 3.0-3.1. Glass luster. Perfect cleavage in one direction. Fragile. Euclase is an extremely rare mineral, which is found in the shape of columnar and, more often, thick-table crystals about 2.5 cm. Transparent to translucent. Color: more often colorless, white, sometimes yellow, yellowish-green, light bluish-green, emerald-green, blue or violet. Green color depends on the admixture of chromium (Cr3+), light blue one – on ions of iron. Light blue euclase displays pleochroism from light bluish-green to rose, and to colorless. With the method of irradiation colorless crystals of euclase can be transformed into light blue ones.

Deposits. Euclase is a typical mineral of granite pegmatites, greisens and more rarely alpine veins. In Russia, euclase is rather well known gemstone. It was discovered in the South Urals, on placers of the Kochkar’ gold-ore deposit in 1858. The biggest crystals were extracted from placers on the Sanarka River and its tributary – the Kamenka River, at the near Plast town. The biggest transparent polychromatic crystal of euclase from that place, 73x20x14 mm. in size, is kept in the Mining Museum, SPb. In 1997, the crystal in size 18x7x6 mm named “The Star of Russian Brazil” here was found. In the Middle Urals, at Izumrudnye Kopi, they found greenish crystals of euclase up to 35x40 mm. In the Western Sayan Mts., at the Raduga deposit, in muscovite-fluorite metasomatic rock they found well-formed crystals of euclase up to 3 cm. long. Its findings are also known in the northwest of the Rep. of Tyva and in East Transbaikalia. In the Khabarovsk Region crystals of euclase were discovered in the upper reaches of the Uchur River, in the Dzhugdzhur Ridge; and also in the Primorskiy Region – at the Pogranichnoye deposit, in the Vladivostok Region. In Uzbekistan, it was found at the Sargardon deposit, in the Chatkalskiy Ridge. In other countries, euclase was discovered in Sweden, in pegmatites of the Kolsva deposit, Västmanland; and in the south of Norway – in the region of Iveland. In the north-west of Zimbabwe euclase up to 8 cm., of intensive light blue color, was found in a pegmatite vein at the Last Hope deposit, near Miami, Karoi Dist. In Tanzania, it was discovered in green and light blue crystals up to 7x3 cm. at the Mikese deposit, in the region of Lukangasi, Morogoro Dist. Findings of gem-quality euclase are known also in Mozambique, in pegmatites of the Alto Ligonha region, De Nampola Prov.; in Madagascar as colorless crystals up to 3 cm. at Mahasolo; also in Congo, Kinshasa (form. Zaire), in the form of sapphire-blue crystals. In India, euclase is found in pegmatites together with tourmaline in the northern part of the Jammu and Kashmir State (disputed area), near Gilgit.

In the U.S.A., in Colorado, at the mines Boomer and Redskin Gulch, Park Co., they found small crystals of pale blue euclase. In Brazil, gem-quality euclase in crystals up to 6 cm. and in their clusters up to 9x5 cm., is extracted at the deposits: Boa Vista, Villa Rica, Santa do Encoberto and in the region of Diamantina, Minas Gerais. In the Oro Preto Region transparent crystal 10 cm. at the Dom Bosco deposit, were found. In the same state, they found the biggest non-transparent crystal of light bluish euclase in 750 gm. In the Rio Grande do Norte State, occur colorless, red and light-blue euclases. In Colombia, greenish-light blue euclase crystals up to 15 cm. occur at the emerald deposits Chivor and Gachala. In Ecuador, it was found at the Alto Momoz deposit.

Synonyms. Oriental aquamarine | Chrupik, Old Russ. | Prismatic emerald | Euclasite.

Treatment. Euclase was brought to Europe for the first time from Peru in 1785. Excellent cleavage makes it difficult to process it. It is faceted mainly with the step pattern. In this case light blue and green gems are rarely more than 2-3 ct.; but gems of other colors can reach more than 5-6 ct. From Brazilian rough material they make faceted gemstones up to 25 ct. In the Smiths. Inst., Wash., there are three faceted euclases from Brazil: a green one in 12.5 ct., a yellow one in 8.9 ct. and a light bluish-green one in 3.7 ct. In the Museum of Calgary, Canada, there are also Brazilian euclases: a colorless one in 15.43 ct. and a green one in 14.0 ct.

Similarity. Euclase looks like aquamarine, noble beryl, hiddenite and light blue sapphire.