Vallerano Quarries, Valleranello, Rome, Metropolitan City of Rome Capital, Lazio, Italyi

Regional Level Types
Vallerano Quarries	Group of Quarries
Valleranello	Urban area
Rome	City
Metropolitan City of Rome Capital	Metropolitan City
Lazio	Administrative Region
Italy	Country

Two adjacent quarries on both sides of Via Laurentina road at km 11, between Vallerano and Valleranello.
Nenni (formerly CO.BI.LA.) quarry and Covalca quarry, located respectively to the east and to the west of Via Laurentina, are opened in an outcrop of the Vallerano lava flow, one of the lava flows of the Vallerano-Acquacetosa lava plateau (460±4 ka; Karner et al., 2001), which lies over the "Pisolitic Tuffs succession" and comprises a thick (30-50 m) sequence of fissural lava flows (Vulcano Laziale period of activity of the Colli Albani Volcano). The quarried lava is classifiable as melilite- nepheline-bearing leucititic lava.


The rock frequently holds small cavities containing calcite, often associated with zeolites, fluorapatite, and vonsenite; moreover calcite is present in form of veins and is also noticeable under a microscope dispersed in the groundmass, often surrounding leucite and nepheline crystals. Some minerals have also been found in xenoliths, trapped in the lava flow.


From a mineralogical point of view, cahnite and zeolites are the most known minerals for these quarries.

Cahnite is probably a mineral formed at the last stage of hydrothermal phase. It appears as tetragonal bisphenoids with sharp edges and the (111) faces often slightly curved. Crystals showing a hopper-type growth are very rarely found. Crystal twinning frequently occurs. Cahnite crystals are always very transparent and brilliant; their colour varies from pale yellow to orange; their size is usually in the range 0.3-10 mm.

Gismondine (de facto gismondine-Ca) appears as milky or rarely transparent pseudotetragonal dipyramids, rarely exceeding 10 mm in size. Typically associated minerals are K-rich chabazite and phillipsite, with which the gismondine is often inter- and overgrown; in the K-rich phillipsite - gismondine intergrowths, gismondine and phillipsite are intimately associated and not morphologically distinguishable.
A gismondine sample from Vallerano resulted the richest in K (0.31 a.p.f.u.) of all known gismondines (Vezzalini & Oberti, 1984), much less, however, than the previous values published for Vallerano and other leucitites from Rome area. For instance, Zambonini (1902) reported for the Vallerano gismondine a higher K content (0.74 a.p.f.u.); it has to be ascribed to the erroneous analysis of phillipsite-gismondine intergrowths, which led to a high K value.

In most, if not all cases, K-rich chabazite is ascribable to chabazite-K. Its white pseudorhombohedral crystals are generally twinned and form lens-shaped crystals (phacolite variety), often grouped into rosettes and spherical aggregates rarely exceeding 10 mm in size. Some chabazites show a vivid green fluorescence under long-wave UV light. Typical associated minerals are K-rich phillipsite, fluorapatite, vonsenite, calcite, aragonite, augite, magnetite, cahnite, and gismondine. Yellow or colourless pseudocubic crystals have been observed in cavities inside metamorphosed xenoliths.
A chemical analysis by atomic absorption spectrometry of milky spherical aggregates of twinned chabazite-K crystals (K 1.36 a.p.f.u., Ca 1.04 a.p.f.u., Sr 0.40 a.p.f.u., Na 0.28 a.p.f.u.) from leucitite is reported by Passaglia (1970). A wet chemical analysis of a K-rich Ca-dominant chabazite is reported by Zambonini (1902). As no particular paragenetical order among chabazite, phillipsite, and gismondine has been observed at Vallerano, it is possible that a chabazite with such composition grew from K-rich hydrothermal solutions more depleted in K than those from which K-dominant phillipsite and chabazite originated. However, the contamination of the analysed sample with associated gismondine, which led to a high Ca value, cannot be excluded.

In most, if not all cases, K-rich phillipsite is ascribable to phillipsite-K (Zambonini, 1902; Gualtieri, 2000). Its colourless crystals, always twinned, form pseudo-orthorhombic prismatic crystals, commonly elongated along the a-axis; blocky, equant crystals and fan-like to spherulitic radiating aggregates are common, as well as the typical cruciform penetration twins. Typical associated minerals are K-rich chabazite, fluorapatite, vonsenite, calcite, aragonite, augite, magnetite, cahnite, and gismondine. In the phillipsite-gismondine intergrowths, the two minerals are intimately associated and not morphologically distinguishable.
A chemical analysis by atomic absorption spectrometry of a K-rich Ca-dominant phillipsite (K 1.91 a.p.f.u., Ca 2.02 a.p.f.u.) is reported by Galli & Loschi Ghittoni (1972). As no particular paragenetical order among chabazite, phillipsite, and gismondine has been observed at Vallerano, it is possible that a phillipsite with such composition grew from K-rich hydrothermal solutions more depleted in K than those from which K-dominant phillipsite and chabazite originated. However, the erroneous analysis of phillipsite-gismondine intergrowths, which led to a high Ca value, cannot be excluded.

Fossils

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References