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The Black Stone of the White Nights

St Petersburg is, by many reasons, the peak of the summer solstice. Regardless of what they might say, people come here not for the natural phenomenon of the White Nights (as the days are even brighter in Murmansk) but for the magic of the "patterns of the cast-iron fences". This, as much in Russian history, would be impossible without Alexander Pushkin, without master foundry workers and without the main component of the aerial lattices.

This natural mineral has been known to science for more than two centuries. In 1982, however, it was removed from the catalogue of the International Mineralogical Association. Nevertheless, it has an irreplaceable place in the history of metallurgy. Psilomelane (Greek for 'black smooth') is sometimes also called 'bald-headed devil' because of its shiny surface. But it is not known to have any mystical or ominous properties.

Over time, scientists have discovered that psilomelane is not a separate type of mineral, but a group of compounds that share a common structure and composition. For that reason, its name has been removed from the mineralogical catalogue, but among professionals, it has remained as the name of a group of minerals containing manganese that have a complex, inconstant composition and are prone to forming crystalline clusters.

псиломелан
© Форпост Северо-Запад / Горный музей

The mineral is a solid solution of irolusite, manganite and other manganese oxides with water and contains iron, barium, calcium and other elements. Psilomelane has an interesting feature: in a long contact with air, the stone begins to lose bound water and transforms into a pyrolusite substance, the structure of which resembles a black sooty mass, almost resembling a sponge.

The term was first coined by Johan Wallerius, a Swedish chemist and member of the Royal Academy of Sciences. He has made a name for himself in the world of science by introducing a system of chemical classification of minerals. In the winter of 1776 Wallerius was elected an honorary member of the Imperial Academy of Science and Art in St Petersburg. The largest psilomelane deposits are located in Georgia and in the south of Ukraine, in the Nikopol manganese ore basin. In Russia, it is mined in the Murmansk and Tyumen regions, and of course in the Urals.

псиломелан
© Форпост Северо-Запад / Горный музей

The mineral serves as an ore raw material from which mirror iron and ferromanganese are made. These alloys are used to make decorations for buildings and fences, as well as decorative artistic objects such as statuettes, candlesticks and paperweights.

The East is known to be the birthplace of the iron foundry industry. But already in XIII century artistic craftsmanship in cast iron became the property of Europeans. The oldest examples of such castings from the XVI and XVII centuries are ornamental plates of floors in Catholic cathedrals, doors and tombstones.

In Russia, iron castings date back to the casting of staircase railings, doors and window grilles. The first blast furnaces were built in 1632 near Tula - the famous Gorodischenskie factories, where the industrial production of cast iron and iron alloys on its basis was established for the first time in the country. The process was set in motion by a grant from Alexei Mikhailovich, which allowed them to "cast and forge iron and iron alloys: "to cast and forge cannons, cannon balls, boilers, planks and various bars; and to do all sorts of ironwork".

доменная печь
© Форпост Северо-Запад / Горный музей

Gradually, "domestic" cast iron became popular. Foundry workers began to be commissioned for the decorative elements of buildings, fireplaces and cast-iron stove doors in houses. Intricate bas-reliefs and statues were used for the decoration of various architectural ensembles. Balconies, railings, gate posts and gate sashes and lampposts were made of cast iron.

фонарь
© Форпост Северо-Запад

By the end of the 18th century, the use of iron castings becomes even more widespread. Massive lattices and openwork fences replace wrought iron fences. They were increasingly used for the creation of arbours and pavilions in parks and gardens. The fences on the embankments of the Neva, the Smolenka, the Karpovka, all the main canals in the empire's capital and bridges began to be used en masse.

ограда набережная
© Форпост Северо-Запад

Speaking of iron alloys involving psilomelane, it is impossible not to think of Kaslino castings. Its history began in 1747, when the Tula merchant Yakov Korobkov founded the Kaslinsky ironworks and ironworks in the Southern Urals.

касли
© Форпост Северо-Запад / Горный музей

The middle of the 19th century was the heyday of artistic iron casting. During this period, the Kaslino factory received the Small Gold Medal of the Free Economic Society in 1860. The factory participated in exhibitions in St. Petersburg, Nizhny Novgorod, Paris and London. Cast iron is widely used in his work by the Italian architect Rossi and the Russian Stasov. In Moscow, the Arc de Triomphe and the Alexandrovsky and Neskuchny Gardens were equipped with cast-iron statues.

Psilomelane is highly prized by jewelers and decorative artists despite its brittleness, gloomy appearance and strange name. It is also used as an ornamental stone, including for imitating hematite. The dendrites of psilomelane lend a picturesque decorative quality to coloured stones.

псиломелан
© Форпост Северо-Запад / Горный музей

Today ferromanganese is used mainly as an alloying additive to increase the density of steel. The secret of Demidov's "Old Sable", which at one time displaced Swedish iron from the European market, is still unresolved. However, scientists are absolutely sure that no additives in the form of "mirror iron" were used. So, psilomelan was also involved in the history of Catherine's victories "in the times of Ochakov and the conquest of the Crimea".