The rock is phonolite
, and is divided into irregular columns.
These units are overlain by the Oligo-Miocene rocks comprising silicified and altered trachytic tuffs as well as fresh intrusive alkaline trachytes and phonolites. [.sup.40.A]r/[.sup.39A]r geochronological analyses of sanidine crystals from the phonolites have yielded an age of 25 Ma (Late Oligocene-Early Miocene) for the alkaline volcanic rocks (Sarifakioglu et al., 2009).
Twenty-nine sediment samples and twenty-nine rock samples were collected along creek valleys that transect the metamorphites, phonolites, trachytes, and pegmatites (outside the study area) in compliance with the principles of geochemical prospecting.
are characterized by phenocrysts of leucite-pseudomorphs, alkali feldspar ([Or.sub.47-75]), clinopyroxene ([Wo.sub.48-50][Fs.sub.11-34]), Fe-pargasite, and nepheline [+ or -] biotite [+ or -] titanite [+ or -] melanite (Ti-andradite up to 68 wt%) [+ or -] magnetite or haematite.
Reactions which affect water chemistry in Post Roque Nublo, Roque Nublo, and phonolites
aquifer-rocks were defined and quantified.
On the basis of the chemical composition and relict primary mineralogy, Vard and Williams-Jones (1993) concluded that the sill rocks are more appropriately classified as altered agpaitic phonolites
Krutsky, N.: 1989, Phonolites
: Research and forecast evaluation on non-traditional industrial raw-materials, MS Geoindustria Praha (in Czech).
Plagioclase dramatically removes Sr at intermediate stages and alkali feldspars sequester Ba and Rb as late-stage trachytes and phonolites
form in alkaline magmas.
The extreme continentality and high altitude lead to very severe conditions and create an unusual climate, especially in the central region of Atakor, which is dotted with steep igneous extrusions (phonolites
(1992) The regional geology of the Pocos de Caldas alkaline complex: mineralogy e geochemistry of selected nepheline syenites e phonolites
. Journal of Geochemical Exploration 45, 25-51.
The members of the group are most frequently found in association with nepheline or leucite in nepheline syenites or phonolites
and related undersaturated rocks.
The rock types found at Monte Somma/Vesuvius are largely leucitites and phonolites
, both of which are high-soda volcanic rocks.