Valbrutta (Val Brutta), Lanzada, Sondrio Province, Lombardy, Italyi

Regional Level Types
Valbrutta (Val Brutta)	- not defined -
Lanzada	Municipality
Sondrio Province	Province
Lombardy	Region
Italy	- not defined -

Minerals are found in serpentinite at various sites, such as the old asbestos mines, serpentinite quarries, and serpentinite block accumulations.

Andradite var. demantoid and chrysotile are the most known mineral from Valbrutta. In particular, small emerald-green crystals of demantoid with fibrous asbestos (chrysotile), and sometimes in association with calcite, have been found in the old asbestos mines, called “dei Puntesci”, located at an elevation of 1570 m, in the little valley descending from Ristoro di Franscia at Dossi di Franscia (1650 m) towards Valbrutta (Gramaccioli, 1962). Asbestos specimens, with fibres that can attain 30 cm in length, have been recorded from the old serpentinite quarries, named “dei Rive”, located below Ristoro di Franscia, always on the right slope of Valbrutta (Gramaccioli, 1962). Serpentinite blocks from the talus on the orographic left of Lanterna stream, in proximity of the road, have yielded interesting specimens of demantoid, in which emerald-green crystals are disseminated among other ones of yellowish colour (Bedognè, 1970 and 1979).
Hydrated magnesium carbonates are sporadically found inside serpentinite fissures. Six years earlier the official description of artinite from Dossi di Franscia (type locality), Luigi Brugnatelli already studied an identical hydrated magnesium carbonate (Brugnatelli, 1897 and 1899) which he personally collected in Valbrutta (Val Brutta). From the chemical analysis he deduced the formula MgCO3•Mg(OH)2•3H2O, but, due to the scarcity of the analysed material (0.171 g including impurities), Brugnatelli thought it was prudent to wait for a new analysis before recognising the mineral as a new species. The new analysis, that he performed on the abundant material found in 1902 at Dossi di Francia by Pietro Sigismund and forwarded through Ettore Artini, confirmed the identicalness of the two finds. Artinite has also been found in recent times at the serpentinite quarries.
Carbonate veins (hydrothermalites) in serpentinite are the source of various interesting minerals, such as: dolomite, chrysotile, magnetite, copper, cuprite, and malachite at the ancient municipal asbestos mine of Valbrutta (located below Ristoro di Franscia on the right slope of Valbrutta); dolomite, calcite, quartz, rutile, anatase, ilmenite, chlorite, talc, and sulphides at the serpentinite quarries on the orographic left of Lanterna stream; dolomite, calcite, sulphides, magnetite, rutile, anatase, and apatite in the serpentinite block accumulations of the Lanzada-Campo Franscia road works dumped at Valbrutta and Campo Franscia (Franscia).
Furthermore, titanian hydroxylclinohumite-forsterite-calcite veins are not rare in serpentinite of this area (Trommsdorff and Evans, 1980; Bedognè et al., 1993; Bedognè et al., 2006).

Notes:

“Ti-bearing clinohumite; titanclinohumite”: according to the analyses performed, this mineral in the Malenco valley serpentinite is practically fluorine-free (Trommsdorff and Evans, 1980). Therefore, after institution of the new species hydroxylclinohumite in 1999, all records of “titanclinohumite” in the antecedent literature and all specimens preserved in public and private collections consequently labelled are now Ti-bearing hydroxylclinohumite (Bedognè et al., 2006).

“Mauri quarry”: one of the three active serpentinite quarries at Valbrutta is operated by the company Marmi Mauri S.r.l.. As the same company operates three serpentinite quarries in the municipal territory of Lanzada (at Le Prese, Valbrutta, and Dossi di Franscia respectively), some confusion can arise about the exact provenance of specimens simply labelled as from “Mauri quarry, Lanzada”. Nevertheless, the name Mauri quarry has been generally used among the mineral collectors to indicate the one located at Le Prese (http://www.mindat.org/loc-233994.html), where vesuvianite-rich rodingite dykes have been evidenced.

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References