Within the rhyolites of S. Vincenzo volcanic district, both sedimentary and magmatic enclaves sporadically occur (Ferrara et al., 1989). In this study, two kinds of magmatic inclusions with "volcanic" textures have been recognised. No evident chilled margins are present at the host-enclave contact, possibly due to a low temperature contrast between the two melts. The groundmass of the enclaves is less glassy and grain size of the microlites is greater than that of the enclosing rhyolite.
Type I enclaves: rounded, with variable sizes (from few mm to 40 cm); spherical vesicles are present, sometimes filled with secondary minerals; their distribution is homogeneous throughout the whole enclaves. The contacts with the host lava are sharp and lobate. The enclaves are sub-aphanitic, with Pl and very minor Opx phenocrysts; rare relics of iddingsitized olivine are sometimes present.  Embayed quartz of possibly xenocrystic origin often occurs. Plagioclase always shows an inner spongy rim, which sometimes extends towards the core; clear, thin outer rims are also present. Opx is highly corroded and altered. The groundmass is composed by Pl, Cpx, opaques and minor Bt.
Type II enclaves: rounded to ovoidal, with size up to 10 cm; vesicles are present, with smaller size and more irregular shape than type I; their distribution is homogeneous throughout the whole enclaves. Contacts with the host lava are sharp, with lobate to cuspidate shape. Type II enclaves are more porphyritic, with phenocrysts of Pl, Bt, Cpx, Opx. Embayed quartz and relics of iddingsitized olivine often occur. Plagioclase has a spongy rim thinner than that occurring in type I feldspars; tiny clear outer rims are rare. Biotite occur both as phenocrysts and microphenocrysts, the former being sometimes embayed. Opx and Cpx form glomerocrysts; some crystals are corroded; some Cpx crystals are zoned. The groundmass is composed by Bt, Pl, Kfs; small glass blebs occur.
Type II inclusions were classified as latites (Ferrara et al., 1989). Type I, because of their subalkaline affinity and the occurrence of plagioclase and minor orthopyroxene phenocrysts, are best classified as basaltic andesites and andesites.
Type I enclaves are metaluminous, and in a K2O vs. SiO2 diagram fall between the high-K calc-alkaline and calc-alkaline fields. Mgv is always lower than 60 and the K2O/(K2O+Na2O) ratio ranges form 30% to 48%, indicating a prevailing sodic character. Incompatible trace elements (e.g. Zr, Th, Ba, Sr) are lower than type II, while comparable amounts of compatible elements are present.
Type II enclaves are metaluminous to peraluminous, and belong to a shoshonitic series. MgO is often higher than 3%, and the K2O/Na2O ratio is in the range 1.5-2.5, on the border towards ultrapotassic rocks (Foley et al., 1987); however, the Mgv is lower than typical values occurring in ultrapotassic latites (Innocenti et al., 1992). With respect to type I, these enclaves are slightly richer in silica, and have higher  K2O, P2O5, Zr/TiO2, and lower TiO2, Al2O3, CaO and Nb/Y.
Compared to other latitic lavas occurring in Central Italy, type I enclaves differ mainly for lower K2O/Na2O ratio and higher Ca, Ti and Fe contents. Type II are more similar, even if they show slightly lower K2O/Na2O and higher Fe and P.
Variation diagrams and mass balance calculations rule out the possibility that latitic and andesitic magmatic inclusions belong to a single evolutionary trend, neither by fractional crystallisation, nor by a mixing process in which the host rhyolite is one of the end members: type I and II enclaves evolved from two different mantle-derived magmas. Mixing processes with the enclosing lava are evident only for type II, for which hybrid compositions have been found, as well as some crystals which could have been incorporated from the host: isotopic data on type II enclaves (Ferrara et al., 1989; Feldstein et al., 1994) pointed to an isotopic disequilibrium among phenocrysts and between phenocrysts and groundmass, interpreted as a mixing process between enclaves and host rhyolite. Petrographic and geochemical (major and trace element) evidence of mixing between the host lava and type I enclaves has not so far been found.