Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia



BRUCITE (Brucit—Brucite—Ѕрусит) (Bruce, A. 1814), after Archibald Bruce (1777-1818), physician and professor at Yale University, the U.S.A., a discoverer of the mineral.

Composition & Properties. Hydroxide – Mg(OH)2, trigonal system. Hardess 2.5-3. Density 2.4. Glass luster to pearl one. Cleavage in one direction. Flexible. Brucite is widespread. It is found as thick plate crystals, and alas well as massive fine-flared and fine-fibrous aggregates – fibrous brucite. Such rock as brucitite is composed with it almost completely. According the specifics of their texture, massive varieties of brucite are classified at stripped, lense-stripped, and net-veined and breccia ones. Transparent to translucent. Color: gray-light bluish, greenish-white, brownish or colorless. Manganbrucite with admixture of manganese is honey-yellow to brownish in tone, ferronemalite with content of FeO to 5% and ferrobrucite with content of FeO to 36% become brownish in the light. Additional reason of its color if the effect of light scattering which depends on fine admixture of magnesite.

Deposits. Brucite is formed at the contact metasomatism of rocks of the basic content, low-temperature metamorphism and as veins in serpentinites and in weathering-crusts. In Russia, in the Khabarovsk Region, there are the largest deposits of this stone: Kul’durskoye – in the Malyi Khingan Ridge, and another one near the Izvestkovaya railway station. Small volumes of brucite are found in the Krasnoyarsk Region, at the Komsomol’skiy mine, and in the Talnakh deposit. In Yakutia on the Olekma River – blue nemalite; in Pribaikalia, at the Slyudyanka deposit – nemalite; in the Rep. of Tyva, at the Ak-Dovurak massif – nemalite. In 1829, in the Middle Urals, in serpentinite of the Pyshminskiy plant they found crystals up to 3 cm. and aggregates of nemalite with the length of fibers up to 20 cm. At the Bazhenovskoye deposit of asbestos, they found transparent crystals of tender light blue brucite up to 15 cm. long and greenish-light blue massive nemalite. At the Sarany mine, white nemalite forms parallel-fibrous aggregates with the length of fibers up to 30 cm. In the South Urals, nemalite is known at the Satka magnesite deposit and at the Bashartskiy mine near Beloretsk. In Kazakhstan, to the east from Aktiubinsk (now Ak-Mola), there is the Donskoye brucite deposit of near the Chrome-Tau Ridge. In Armenia, brucite was discovered at the Shorja deposit near Sevan Lake. In Italy, at the Carro deposit, Liguria Prov., brucite was discovered as mighty veins. In Africa its deposit is exploited in Zimbabwe – the Ethel mine near Mutorashanga (Mtoroshanga). In the U.S.A., in Pennsylvania, at Woods Mine of the Lancaster Co., they extracted the most beautiful, snow-white crystals of brucite up to 20 cm. in cross-section and brucite marble. In the AMNH, N.Y., there is a crystal of brucite from that region, 14x8 cm. in size. Significant deposits of brucite are situated in Nevada, to the east from Gabbs locality. In 1983, in Canada, at the Jeffrey Mine, near Asbestos, they found translucent jewelry-ornamental nemalite with the length of fibers more than 50 cm. From crystals of light blue brucite from the Madock deposit, in the region of Bancroft, they received faceted stones up to 4 ct.

Synonyms. Hydrophyllit | Hydrotalc | Magnesine, after the content | Manganbrucite, after the content | Nemalite, from Gk. “nema” – a thread, after the shape of its crystals; syn. amianthoide | Shepardite | Water talc | Texalith, after the discovery location in Texas, the U.S.A.

Treatment. As an ornamental stone, brucite is close in its properties to agalmatolite – it is well polished and is cut in cabochon. It is used also in stone-carving. As an ornamental stone, brucite marble with the content of brucite up to 80% is of special interest; it is known in Russia, in the Khabarovsk Region, at the Kul’durskoye deposit; and in the South Urals, at the Bakal’skoye and Satka deposits. In North Italy, near Predazzo similar brucite marble with the content of brucite up to 34% and with admixture of calcite and periclase is known under the trade name pencatite or predazzit.

Similarity. Brucite looks like alunite, gibbsite, pyrophyllite and talc.