The minerals of Traversella

Sentences without a label are documented facts; the others are marked "probable" or "uncertain".

In a few square kilometres Traversella has one of the highest concentrations of mineral species in the world. For the miners what counted were magnetite, pyrite, chalcopyrite and later scheelite; for collectors the crystals of the geodes and the rare species count too. This page presents the main minerals, those of Brosso and the places where they can be seen.

Ninety-eight species

Today 98 valid mineral species are listed at Traversella. Barelli's catalogue of 1835 cited 18, Strüver in 1869 counted 36 and Torti in 1973 counted 70: each generation has found new ones. A page of the ecomuseum even speaks of 150 types of minerals, without saying how it counts them probable.

The richness comes from the history of the rock: the Traversella system includes the magmatic body, the transformed host rocks, various types of skarn, hydrothermal veins and breccias. Many collectors' specimens, above all from the upper levels, come from the late veins of quartz, carbonates, pyrite, gold and galena. The Gruppo Mineralogico Valchiusella, the mineral club of the Chiusella valley, continues to find in the mine new or rare species and associations, among them cobaltite, erythrite, bismuthinite, silver and tochilinite.

Sources: Costa et al. 2019, pp. 7, 9, 13, 17; Traversella ecomuseum page, «Visita al museo»

Magnetite

Magnetite, Fe₃O₄, is the most widespread and abundant mineral in the Traversella mines: it occurs almost everywhere as a fine-grained mass and was the main object of mining. In the geodes it forms rare crystals, from a few millimetres to several centimetres, dodecahedral or octahedral, with striated faces sometimes covered with talc. Two dodecahedral crystals with sides of more than 12 centimetres, described by Borson in 1830, are in the Museo Regionale di Scienze Naturali, the regional natural science museum, in Turin.

In 1873 Jervis describes the granular magnetite of the deposit in a matrix of dolomite, calcite, quartz and chlorite and gives it a yield in pig iron of 40-50% probable. In the last years, in 1965, the plant produced 6 tonnes an hour of iron concentrate, with a maximum grade of 68% Fe₃O₄.

Sources: Costa et al. 2019, pp. 14-15; Jervis 1873, p. 122; Baldassarre et al. 2025, p. 3

Scheelite and tungsten

Scheelite, CaWO₄, is the tungsten mineral. It occurs in varying abundance at all levels of the mine; the old crystals of more than 10 centimetres come from the highest levels, today inaccessible because of collapses and backfilling. Its classic form is the pseudo-octahedral bipyramid; the large crystals, often enclosed in talc, chlorite or calcite, are yellowish or yellow-orange, with an adamantine or vitreous lustre. It probably formed for the most part during the retrograde skarn probable.

It was first noticed on the shaking tables of the washing plant by the technicians of the Cogne, who from 1937 used FIAT's plant, and their concentrate reached, according to Berattino, about 65% WO₃; in the 1930s it was also found in the waste heaps. In 1965 the plant produced 750 kilos a year of scheelite concentrate, with a maximum grade of 60% WO₃. The scheelite of Traversella also contains rare earths: 1,036 parts per million of light rare earths, between a minimum of 101 and a maximum of 2,125, and 144 of heavy ones, according to Matteucci as cited by Baldassarre and colleagues.

Sources: Costa et al. 2019, pp. 7, 12, 14-15; Berattino 1988, p. 248; Baldassarre et al. 2025, p. 3

Ferro-ferri-hornblende

Since 2016 Traversella has been the type locality of ferro-ferri-hornblende: a dark green amphibole, a new member of the amphibole supergroup, whose holotype comes from the historical collection of L. De Magistris and from retrograde skarns. It is monoclinic, with the formula Ca₂(Fe²⁺₄Fe³⁺)AlSi₇O₂₂₂, and forms greenish or black acicular crystals in a matrix of fibrous tremolite with a little quartz and calcite. The same specimen had been called "speziaite" by Colomba in 1914, in honour of Giorgio Spezia; later the name was discredited and the mineral redefined as hornblende.

Sources: Costa et al. 2019, pp. 13, 15

Other famous minerals

• Amethyst: crystals of more than 30 centimetres, of an intense violet; Pelloux had already found it in 1908 and it was found again in 1959 in a large cavity of the third Ferriere mass.
• Dolomite: when the mine was active it formed crystals of more than 20 centimetres, above all at the contact between the carbonate rocks and the metal-bearing masses.
• "Mesitine": described by Breithaupt in 1828 as a new species with Traversella as its type locality, later discredited and considered iron-bearing magnesite; it forms lenticular rhombohedra up to 5-6 centimetres.
• Cobaltite: identified only recently and studied for the first time in Dalla Costa's thesis; it lies at the southern margins of the Ferriere Masses, linked to magnetite and scheelite. Under the microscope it is white with a pinkish tinge and often contains bismuthinite, native bismuth, pyrrhotite and chalcopyrite; the outcrops are covered with a pink-violet patina of erythrite.
• Native gold: in Dalla Costa's thesis it was found in rare grains inside the cobaltite, in a single section of the second Ferriere Mass.

Sources: Costa et al. 2019, pp. 14, 16; Dalla Costa 2011, pp. 1, 4, 6, 15

The minerals of Brosso

At Brosso the deposits are of pyrite and haematite, the oligist of the old sources, in extensive limestone masses. In 1873 Jervis describes a compact, crystalline pyrite with many crystal forms, generally free of arsenic; the oligist is massive and micaceous, and the baryte, lamellar or in clear crystals, forms the matrix together with pyrite, oligist and siderite probable. Munari also mentions chalcopyrite, carbonates such as siderite, ankerite and mesitine, and a rare boron mineral, ludwigite, of which he shows a specimen from the Vola Gera tunnel probable. Mesitine is very common at Brosso probable. In a pegmatite of the Brosso diorite quarry the smoky quartz, darkened by radioactivity, is for Munari a clue to the presence of uranium probable.

Sources: Novarese 1901, p. 76; Jervis 1873, pp. 118-119; Munari 2019, pp. 25, 106, 108-109

Where to see them

At the Museo della Miniera di Traversella, according to Turismo Torino, more than 300 mineral specimens are on display; in 2017 Costa counted almost 800 uncertain. The two large magnetite crystals described by Borson are in the Museo Regionale di Scienze Naturali in Turin. The Gruppo Mineralogico Valchiusella has published nine Quaderni, booklets, among them Scheelite, Pirite, Cobaltite, I Carbonati and Ametista; its website gives only the titles probable. The miners themselves gave away specimens: in 1970, when the mine was still active, they gave Munari a piece of massive magnetite with chalcopyrite probable.

Sources: Turismo Torino, online page, consulted on 15 October 2026; Costa et al. 2019, pp. 13, 15; Gruppo Mineralogico Valchiusella, page «Quaderni», consulted on 16 October 2026; Munari 2019, p. 105