The Monti della Tolfa or "Tolfa Mountains" are a volcanic group

Volcanic group

A volcanic group is a collection of related volcanoes or volcanic landforms. Note that the term is also used in a different sense when it denotes a suite of associated rock strata largely of volcanic origin; see group for details.-Notable volcanic groups:-See also:*Complex...

 in the Anti-Apennines of the northern part of the Lazio region of central Italy

Italy

Italy , officially the Italian Republic languages]] under the European Charter for Regional or Minority Languages. In each of these, Italy's official name is as follows:;;;;;;;;), is a unitary parliamentary republic in South-Central Europe. To the north it borders France, Switzerland, Austria and...

. They are bounded by the Tyrrhenian Sea

Tyrrhenian Sea

The Tyrrhenian Sea is part of the Mediterranean Sea off the western coast of Italy.-Geography:The sea is bounded by Corsica and Sardinia , Tuscany, Lazio, Campania, Basilicata and Calabria and Sicily ....

 coast to the west, by the Monti Sabatini to the east, and by the Monti Cimini and the Mignone river to the north. Tolfa

Tolfa

Tolfa is a town and comune of the province of Rome, in the Lazio region of central Italy; it lies to the ENE of Civitavecchia by road.It is the main center in the Monti della Tolfa, an extinct volcanic group between Civitavecchia and the Lake of Bracciano....

 and Allumiere

Allumiere

Allumiere is a comune in the Province of Rome in the Italian region Latium, located about 60 km northwest of Rome.Allumiere is traditionally divided into the contrade of Burò, Ghetto, La Bianca, Nona, Polveriera, and Sant'Antonio....

 are the principal towns.

The highest peak is the Monte della Grazie, at 616 m above sea level. The Monti della Tolfa consist mostly of trachyte

Trachyte

Trachyte is an igneous volcanic rock with an aphanitic to porphyritic texture. The mineral assemblage consists of essential alkali feldspar; relatively minor plagioclase and quartz or a feldspathoid such as nepheline may also be present....

s formed during the Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 and the early Pleistocene

Pleistocene

The Pleistocene is the epoch from 2,588,000 to 11,700 years BP that spans the world's recent period of repeated glaciations. The name pleistocene is derived from the Greek and ....

.

The mountains are an important source of alunite

Alunite

Alunite is a sulfate mineral that was first observed in the 15th century in Monti della Tolfa, north of Rome, where it was mined for the manufacture of alum. First called aluminilite by J.C. Delamétherie in 1797, this name was contracted by François Beudant in 1824 to alunite.Distinct crystals of...

, from which alum

Alum

Alum is both a specific chemical compound and a class of chemical compounds. The specific compound is the hydrated potassium aluminium sulfate with the formula KAl2.12H2O. The wider class of compounds known as alums have the related empirical formula, AB2.12H2O.-Chemical properties:Alums are...

 is extracted. The mineral was discovered there in 1461, and extensively mined until the mine closed in 1941, after almost 500 years; for much of this time it was the principal source of alum in Europe.

The Tolfetano

Tolfetano

The Tolfetano or Cavallo Tolfetano is a breed of horse from the northern part of the Lazio region of Italy. It is indigenous to the Monti della Tolfa range of hills which lie within the Maremma Laziale, and which give the breed its name...

breed of horse originates in the area, and takes its name from it.