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Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia

A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

EPIDOTE


EPIDOTE (Epidot—Epidote—Ёпидот) (Haüy, R.-J. 1801), from Gk. “epidosis” – increase, because the base of the rhombohedral prism has one side longer than the other.

Composition & Properties. Silicate – Ca2(Fe3+,Al)Al2[O|OH|SiO4|Si2O7], subclass diorthosilicates, monoclinic system. Hardness 6.5-7. Density 3.2-3.5. Glass luster. Perfect cleavage in one direction. Fragile. Epidote is found in the form of columnar or needle crystals, spheroid aggregates and as grained masses. Color: light green to dark green, yellow, brown to black. Transparent to translucent. There are several varieties of it: sodium-lithium-containing – puschkinite with strong dichroism, chrome-epidote or tawmawite (tawmanite) and vanadium-containing mukhinite; cerium and thorium-containing – orthit. Epidote is characterized with pleochroism from green to brown to yellow. As needle inclusions in rock crystal, it forms quartz hair stone, and quartz, enriched with small short-columnar crystals of epidote in the Urals has the local name ukropnik quartz, because of inclusions of needle crystals epidote similar to fennel. Fine-fibrous mineral inclusions in epidote lead to chatoyancy, because of which it displays the effect of cat’s-eye in cabochon. Among epidote-containing rocks, the most bright and popular ornamental stone is epidosite. It is a rock of metamorphic or hydrothermal origin, composed mainly with epidote and quartz. As an ornamental stone, they use also epidote granite – unakite.

Deposits. Epidote is formed at deposits of magmatic, metamorhphic and hydrothermal genesis. In Russia, epidote was described at first in the Middle Urals before its official discovery, even in 1773, as green schorl. There, they often find its transparent crystals of rather large size. Besides, they discovered non-transparent crystals of puschkinite up to 10 cm. in size at the Katsna Yama mine, in the region of Pervoural’sk; and at the Palkina mine, near Verkhne-Neyvinskiy Zavod, Yekaterinburg Region. In the South Urals, at the Kusinskoye deposit, crystals of epidote reached 15 cm., and at the Nikolaevo-Maximilianovskaya mine – up to 40 cm. long. Transparent puschkinite was found at the Akhmatovskaya mine – both small and large crystals up to 10 cm. long. There, they found also symmetrically developed crystals of green-black epidote – bucklandite.At the Zelentsovskaya mine near Zlatoust, crystals of epidote reached 40 cm. long. An ornamental variety of quartz with inclusions of small crystals of epidote is ukropnik quartz, as well as quartz hair stone, which were extracted at the Gorbunovskoye deposit, near Nizhniy Tagil. In the south of the Kola Penin., near the Turiy Mys (cape), they discovered an ornamental epidote rock of the type of unakite granite. A rock of the similar type was discovered also in the Ukraine, in the Dnepropetrovskiy Region. There, by the village of Dibrovo, they found ornamental epidosites. In Georgia, in the region of the Kazbek Mt., in alpine veins, they found collection crystals of quartz with inclusions of needle crystals of epidote. In Azerbaijan, epidote is a typical mineral for the Dashkesan deposit. In Kazakhstan, numerous findings of gem-quality epidote and its collection druses are known at the Kurzhunkul’ deposit, and at the Aktas deposit epidote is found as inclusions in quartz. Similar samples were extracted in Uzbekistan, at the deposits Ugam and Kattang. In Tadzhikistan, in the East Pamirs Mts., at the deposits Shatput-Say, and Bel’ Al’ma, Zorburulyuk River, they found well-formed crystals of epidote up to 5x5 cm. In Mongolia, at the Altan Khuduk deposit, they discovered transparent dark green crystals of puschkinite up to 10x3 cm. in size, with the effect of cat’s-eye in cabochon – puschkinite cat’s-eye. Besides, there is known the Ongot Tologoit deposit of puschkinite.

In Austria, at the Knappenwand deposit, Salzburg, they extracted the best in the world transparent crystals of epidote. Their size reached 80 cm. long and 8 cm. in cross-section. They typically displayed pleochroism – from brown to green. A bit smaller in size but also transparent dark green epidotes are found in alpine veins of Switzerland – near St Gothard; and in France – at the Cevins deposit, Savoie Dept., Rhône-Alpes, and at the Bourg d’Oisans deposit, where they have the local name delphinite or thalite. In Italy, findings of noble epidote were registered at the deposits Ala Valley and Traversella, Piedmont. In Bulgaria, similar crystals of epidote, 25x15x5 cm. in size, were found at the Kamilski Dol deposit. In Norway, transparent crystals of epidote – arendalite are extracted as additional material at the iron-ore Arendal deposit. In Finland, at the Mekkivaara deposit, near Outokumpu, they discovered crystals of chrome-epidote – tawmawite, and in the region of Iisalmi they extract epidote quartz as an ornamental stone. Ornamental epidote granite – unakite was discovered in Germany and Ireland, and in Finland it is known by Helsinki under the trade name helsinkite. In Greece, crystals of epidote up to 5 cm. is extracted at the Xanthi deposit.

In Africa, gem-quality epidote was discovered in Kenya and on Madagascar. In Mali, at the Sandare deposit, they extract its crystals up to 5 cm. long, in Namibia – up to 6 cm, in Angola, at the Katima Mulilo deposit – up to 7 cm. In Zimbabwe, in the Fungwe Region, they extracted chrome-epidote, as well as epidote-granite – unakite. In South Africa, at the Messina mine, Northern Prov., they find crystals of epidote up to 10 cm., it displays the effect of cat’s-eye in cabochon; and by Keymes they extracted the ornamental rock epidote – okkolite resembling unakite. At placers of Sri Lanka they extract golden-brown epidote, available for faceting. It is found also at deposits of Korea and Japan. In Myanmar, in the region of Taw Maw in the Kachin Mts., together with jadeite they extract chrome-epidote – tawmawite. Transparent, thick green crystals from this deposit, up to 10 cm. long, are exhibited in the Sorbonne. Collection Univ. Paris. Recent years, gem-quality greenish-brown epidote crystals, up to 10 cm., comes from Pakistan, but they are extracted in India, in the Jammu and Kashmir State (disputed area), at the deposits Haramosh Valley, Tormiq, Turnik Nala, Alchori and Ashudi, near Skardu. It is represented with transparent crystals up to 16 cm. long.

In the U.S.A., crystals of epidote, up to 20 cm., available for faceting, are extracted in California, at the deposits Garnet Hill, McFall and Ramona. On Alaska, on the Prince of Wales Is., at the deposits Jumbo, Copper Mountain, Green Monster and others, in cavities among garnet-pyroxene skarns, they find translucent, yellowish crystals of epidote up to 12 cm. long, more than 1 kg. in mass. In Idaho, epidote crystals of epidote up to 30 cm. from the Seven Devils Dist., Adams Co., were found. In Colorado, at the iron-ore Calumet deposit, near Salad, in cavities of quartz veins, they found transparent crystals of epidote up to 15 cm. long, from light green to dark green color. In Nevada, at the Julia mine, there are transparent thick green epidote crystals of the same size in pockets among skarns. In the U.S.A., there is such epidote-containing ornamental rock as copper rhyolite with cuprite from the region of South Mountain, Pennsylvania; and purple epidote basalt – creolite. Another epidote-containing ornamental rock is unakite – epidote granite of rose-green color, composed mainly with quartz, rose feldspar and green epidote. It was found for the first time in North Carolina, at the deposits Blue Ridge and Unaka Ridge; then it was discovered in the Unaka Mts., Tennessee; in Virginia and Georgia. At the gemstone and jewelry show in Tucson, the U.S.A., in 1997, a piece of ore with such crystals of epidote, 70x70 cm. in size, was evaluated in $45,000. Pieces of ore with crusts of small epidote crystals from the Green Monster deposit, Alaska, were evaluated up to $2,200 at the same show. Significant volume of gem-quality light yellow epidote crystals up to 11 cm., including those with the effect of cat’s-eye, comes to the world market from Brazil, Minas Gerais State, Capelinha River and others, near Teófilo Otoni. In Peru, at the Rosario Mabelle deposit and others, they find fan-shaped aggregates of epidote crystals up to 8 cm. long. Epidote available for faceting is extracted at deposits of Mexico, too; and in Peru at the Castrovirreyna Dist., Huancavelica Prov.

Synonyms. Acanticonite (acanticon), from Gk. “akantis” – needle-shaped | Achmatit, after the Russ. mining engineer P.E. Akhmatov | Glassy actinolite | Allochite, obs. | Arendalite (arendite), after the discovery location near Arendal, Norway | Bagrationite, after the Russ. mining engineer P.R. Bagration | Beustite, obs. | Bucklandite, after the Engl. geologist W. Buckland | Escherite, after the Switzerland chemist K. Escher | Oisanite, after the discovery location in Bourg d’Oisans, France | Orthit, from Gk. “orthos” – straight | Pistacite (phistacite), from Gk. “pistaxia” – pistachio, after its color | Chrome-pistacite | Puschkinite (pouschkinite), after M.N. Musin-Pushkin, a curator of the Kazan’ college, where the mineral was described | Rosstrevorite in spherolite aggregates, after the discovery location near Rosstrevor, Ireland | Augite prismatic spar | Strahlite, obs. | Thalite, from Gk. “thallos” – a sprout, after its color.

Treatment. Epidote is rarely more than 5 ct. in the faceted form – another way it seems almost black because of absorption of light. More often, it is cut in cabochons, especially epidote hair stone, ukropnik quartz and epidosite. Epidosite and unakite are extracted as large blocks, they are well polished. They are processed mainly in balls and tumbled stone. In the Museum Hist. Nat., Paris, there is a faceted epidote, 11 ct., from Madagascar; in the Museum of Calgary, Canada, there is a brown epidote 6.9 ct.; in the Smiths. Inst., Wash. – a brown epidote from Austria 3.9 ct.

Similarity. Epidote looks like vesuvianite, clinozoisite, monoclinic pyroxene, hornblende, verdelite and zoisite.

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