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Monte Gelato manganese deposit (Mazzano manganese deposit), Mazzano Romano, Rome Province, Latium, Italy

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Latitude & Longitude (WGS84): 42° 11' 9'' North , 12° 23' 33'' East
Latitude & Longitude (decimal): 42.18611,12.39250
Name(s) in local language(s):Deposito manganesifero di Monte Gelato (Deposito manganesifro di Mazzano), Mazzano Romano, Roma, Lazio, Italia

The small manganese deposit is located near Monte Gelato (it includes the hill known as Le Calcare and extends towards Le Scese locality), right bank of River Treja (Fosso Treja), about 2 km SW of Mazzano Romano (Fornaseri, 1950; Sabella, 1954). This deposit is entirely enclosed in pyroclastic rocks (tuffs) of the «Tufi Stratificati Varicolori de La Storta» (a stratified tuff sequence). It is just one of the over 50 similar deposits occurring in the alkaline volcanic rocks of northern Latium. However, it has been studied in detail, thanks to the presence of a quarry (42°11'9'' N, 12°23'33'' E) that well exposed the stratigraphic sequence (Barrese et al., 1986; Barbieri et al., 1993).

The Monte Gelato deposit formed during Quaternary, probably in the time interval 442 to 230 ky, by water leaching of the pyroclastic rocks. The leaching action was promoted by the presence at that time of a lake in Mazzano area, and developed during two cycles, separated by a sterile phase during which the lake was momentarily filled by new pyroclastic eruptions.

Ranciéite could form owing to adsorbtion of the Mn carried in solution by the water onto hydrous Al minerals (mainly halloysite) which had formed during partial argillation of the pyroclastic pile underneath the lake. Despite being entirely encased within pyroclastic rocks, this manganese deposit is non-volcanogenic in its primary origin nor is related to precipitation from hot geothermal waters; rather, it is typically sedimentogenous, since it derives from adsorption/precipitation of metal solutes contained in the cold ground-table waters at a depth where their redox conditions were turning from reduced to oxidised.

Halloysite and ranciéite coexist throughout the entire «Tufi Stratificati Varicolori de La Storta» formation, but they are missing in the basal ignimbrites. They are particularly abundant in three enriched Mn horizons. Moreover, they also occur in an open fault (as described by Barrese et al., 1986) and in all the fractures crossing the Mazzano sequence. Ranciéite is particularly abundant in the open fault, where it occurs as almost monomineralic stalactites and concretions of fairly large size (2-5 cm).

Mineral List

1 valid mineral.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Pliocene - Miocene
2.588 - 23.03 Ma
Miocene-Pliocene volcanic rocks

Age: Neogene (2.588 - 23.03 Ma)

Comments: May include hypabyssal intrusions.

Lithology: Volcanic rocks

Reference: Geological Survey of Canada. Generalized geological map of the world and linked databases. doi:10.4095/195142. Open File 2915d. [18]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License

This page contains all mineral locality references listed on mindat.org. This does not claim to be a complete list. If you know of more minerals from this site, please register so you can add to our database. This locality information is for reference purposes only. You should never attempt to visit any sites listed in mindat.org without first ensuring that you have the permission of the land and/or mineral rights holders for access and that you are aware of all safety precautions necessary.


Fornaseri, M. (1950) Un deposito manganesifero nei pressi di Mazzano Romano. Rendiconti della Società Italiana di Mineralogia e Petrologia, 6, 96-100.

Sabella, A. (1954) I giacimenti di manganese nelle provincie di Roma e Viterbo. L’Industria Mineraria, 5, 5, 245–248.

Stoppani, F.S., Curti, E. (1982) I minerali del Lazio. Editoriale Olimpia, Firenze, 291 pp.

Barrese, E., Giampaolo, C., Grubessi, O., Mottana, A. (1986) Ranciéite from Mazzano Romano (Latium, Italy). Mineralogical Magazine, 50, 355, 111-118.

Barbieri, M., Barrese, E., Giampaolo, C., Grubessi, O., Mottana, A., Voltaggio, M. (1993) Genesis of the manganese deposit of Mazzano Romano (Latium, Italy). Geologica Romana, 29, 113-129.

Cotterell, T.F., Jenkins, D.A. (2008) Ranciéite from Mynydd Parys, Amlwch, Anglesey, Wales. Journal of the Russell Society, vol. 11, 59-63 (referring to Barrese et al., 1986).

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