Russian Gemstones Encyclopedia

Vladimir Bukanov. Russian Gemstones Encyclopedia



CASSITERITE (Cassiterit—Cassitérite— асситерит) (Pliny the Elder, 77). Known from antiquity, from Gk. “kassiteros” – tin, for its composition.

Composition & Properties. Oxide – SnO2, isostructural with rutile, tetragonal system. Hardness 6.5-7. Density 6.8-7. Diamond luster, greasy one. Fragile. Cassiterite is found as well-formed crystals and as radial-rayed and cryptocrystalline kidney-shaped aggregates of woody tin. Color: yellow, brown, orange, red, green, colorless, gray. In crystals it is transparent to translucent, in cryptocrystalline differences it is non-transparent. Especially beautiful is red cassiterite – ruby tin. Zonal-concentric texture of cryptocrystalline woody tin (holzzinnerz, Germ.) resembles timber. It is well polished, that’s why it can be used as an ornamental stone – toad’s-eye. When admixture of quartz presents in woody tin, it is called silesite. Similar in appearance and also used as an ornamental stone is massive cryptocrystalline hydro-cassiterite of apple-green color.

Deposits. Cassiterite is found in pegmatites, greisens, skarns and ore veins, as well as at placers, which are formed in the process of their destruction. At many such deposits, it is extracted as tin ore, and transparent crystals are extracted as additional material for jewelry purposes. In Russia, in Northern Ladoga Region, at the Pitkaranta deposit, Karelia, they found dark colored crystals of cassiterite up to 5 cm. long. In Transbaikalia, the weight of its crystals in granite pegmatites reached several kilogrammes, and at placers on the Bukhtocha River they extracted woody tin. In the Khabarovsk Region, at the Merek deposit, in the Bureinskiy Ridge, they found crystals up to 7 cm., available for faceting. At the Solnechnoye deposit, they find transparent crystals of cassiterite up to 0.5 kg. In the Malyi Khingan Ridge, at the Dzhalinda deposit they discovered ornamental woody tin. In Yakutia, at the Age-Khaiskoye deposit, in the Yana-Adychanskiy Dist., they registered finding of cranked twin-crystal of cassiterite, 13x10 cm. in size; and at the Kestior deposit, in the basin of the Yana River, they found black cassiterite. In the Magadan Region, at the Dnepropetrovskoye deposit, near the settlement of Myakit, they found woody tin, which received the local name dneprovskite. On the Chukchi Penin. they discovered the Iul’tin deposit of cassiterite, where gem-quality crystals reach 13 cm. long, and the weight of some crystals was up to 32 kg. However, in Russia cassiterite as a gem-quality stone was out of special attention. Crystals of cassiterite up to 10 cm. in size were found in East Kazakhstan, in pegmatites at the Cherdoyak deposit in the Kalbinskiy Ridge, and in Central Kazakhstan, at the Quara Oba deposit. In the south of England, on the Cornwall Penin., there are deposits of cassiterite known from the deep antiquity. At deposits of Spain they found available for faceting yellowish-brown crystals of cassiterite. In Germany, they were found at placers of Saxony, where they received the local name stromzin. In Czech Rep., cassiterite was extracted at the deposits Krupka (form. Graupen) and Horní Slavkov (Schlaggenwald form.). In Portugal, good crystals up to 15 cm. occur at Panasqueira, Caselo Branco. Similar crystals cassiterite was found in Morocco in quartz veins at Oulmès, near Casablanca. In Namibia, at the Small Spitzkopje deposit, near Ressing, they find crystals of cassiterite up to 10 cm. long; and at the Otjimbojo deposit – gem-quality crystals up to 15 cm. At the Spitelman deposit, near Arandiz, as tin ore they extract apple-green arandisite – mixture of hydro-cassiterite and quartz, which was taken for a separate mineral. Pieces of this ornamental material are up to several kilogrammes. From other African countries, where gem-quality crystals of cassiterite are found, we should mention the deposit in Uganda; also in Congo DR, Kinshasa, large cassiterite pebbles and colorless crystals up to 10 cm. or more occurred at Kampene, near Kamitunga, and others deposits of Maniema region.

In Australia, in New South Wales, cassiterite, available for faceting, was extracted at deposits of New England. In Indonesia, gem-quality cassiterite is extracted at placers on the Banka and Belitung Iss., and in Malaysia – on the Malaya Penin.. In China, transparent crystals of cassiterite up to 10x10 cm. in size are extracted in the Sichuan Prov., at the Zinyang deposit, near Pingwu, and in the Guangxi-Zhuang Autonomus Region, such crystals reached the size of 14 cm. Their findings are known also in tin ore deposits of the Yunnan Prov. In Mongolia, crystals of cassiterite up to 6.5 cm. long are extracted at the Bain Mod deposit, Henty Dist., and in the east of Mongolia there is the Modoto deposit of cassiterite. In India gem-quality cassiterite is extracted as additional material from tourmaline pegmatites in the north of the Jammu and Kashmir State (disputed area), in the region of Gilgit. Similar deposits are in Afghanistan, in the Kunar and Laghman Prov., where transparent crystals of cassiterite reach 10 cm.

In Canada, findings of transparent crystals of cassiterite are known on the Baffin Land Is., from where faceted stones up to 24.17 ct. are coming. In Bolivia, at the Araca mine, La Paz Dept.; and Lliallagua, Potosí Dept., they extracted pale colored crystals of gem-quality cassiterite up to 5 cm. long; also Jaco deposit – woody tin. In Mexico, at the Sierra Fria deposit, Aguascalientes State, they extract woody tin. The similar material, available for cabochons, was coming also from the placer deposits Arrohoy Carrisal and Tierra Blanca, Guanahuato State.

Synonyms. Bergzinn, Germ. | Tin garnet | Sighting ore | Tin ore | Silesite, after the President of Bolivia E. Siles | Tin spar | Stannolite | Tin stone | Stromzin, from Germ. “Strom” – a flow | Tennmalm | ~ tin: black~ , mountain ~, needle ~, pryan ~, rosin ~.

Hydro-cassiterite – Tin agate | Tin toad’s-eye | Varlamoffite, after the Belgian mining engineer N. Varlamoff.

Treatment. Cassiterite in transparent crystals is faceted. In cabochons especially beautiful is apple-green arandisite with brown rim, colored with limonite. From pale colored crystals they make sometimes pure stones up to 2 ct., more rarely – up to 5 ct. Pale brown and dark brown crystals are up to 15 ct. in the faceted form; slightly crackled ones – up to 25 ct., mainly from Bolivian rough material. In the Smiths. Inst., Wash. there is yellowish-brown stone 10 ct., and in the Museum of Calgary, Canada, there are brownish ones, 9.51 and 14.85 ct. In private collections there are: a brown stone from Tasmania 9.6 ct., a brown stone from England 11.83 ct. Massive non-transparent woody tin is available for cut in cabochons, which size can be significant.

Synthesis. Synthetic cassiterite is received with the hydrothermal method. Its high index of refraction and obvious dispersion can be compared with those of ruby, rutile and diamond, that are why this material can be evaluated as a perspective one in jewelry.

Similarity. Cassiterite looks like rutile, tourmaline and zircon.