Phonolite

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phonolite

[′fō·nə‚līt]
(petrology)
A light-colored, aphanitic rock of volcanic origin, composed largely of alkali feldspar, feldspathoids, and smaller amounts of mafic minerals.

Phonolite

 

(from the Greek phone,”sound,” and lithos,”stone”), the extrusive equivalent of nepheline syenite. Phonolite consists of feldspathoids (nepheline and other rocks), sanidine, and chromatic minerals (alkaline pyroxene and amphibole). It often contains phenocrysts of hauynite, noselite, and, sometimes, plagioclase. Its texture is usually porphyritic. The cleavage is laminar; individual plates of phonolite ring strongly when struck with a hammer (hence the name). Phonolite is used as gravel in road paving and as an aggregate for concrete.

References in periodicals archive ?
These consist mainly of ankaratrites + (mela)nephelinites (45%) and phonolites (42%) (CominChiaramonti et al.
Phonolites are typically microphyric to hypocrystalline with alkali feldspar phenocrysts or microphenocrysts ([Or.sub.43-83]), nepheline ([Ne.sub.67-79]), occasionally altered to cancrinite, acmitic clinopyroxene (acmite up to 63wt%), and ferroedenite-ferropargasite amphibole.
Two main lineages are apparent for the potassic rock-types (Figure 5 and inset (II)): (1) a silica undersatured lineage (B-P) ranging from basanite to phonolite and peralkaline phonolite and (2) a silica-saturated lineage (AB-T) ranging from alkali basalt to trachyphonolite and trachyte [13,42,44].
Ninety species have been documented from the quarry, mostly from the unique, dawsonite-rich carbonatized phonolite sills which are genetically part of the Monteregian Hills alkaline igneous province.
(1976) and Vard and Williams-Jones (1993) have proposed similar models for the evolution of the phonolite immediately prior to or after it was intruded.
Vard and Williams-Jones likened the autohydrothermal processes in the sills to the phonolite having "stewed in its own juices." Local variations in temperature and solution chemistry resulted in a highly variable mineral assemblage and an often complex mineral paragenesis in the sill cavities, with crystallization of some minerals in two episodes.
Some of the weathered phonolite bodies, buried beneath the Most Basin and covered by Miocene sediments, have been studied in open cast lignite mines.
The phonolite-derived weathering profile on the southern slope of the Marianska hora Hill, forming overburden of an active phonolite quarry, first attracted serious interest in about 1957 (Strnad in Krutsky et al., 1964).
Variations in the [[delta].sup.18]O of Canary islands phonolites and basalts, as well as Icelandic basalts, support assimilation of felsic rocks (e.g., nepheline syenite) from the volcanic edifice (Wolff et al., 2000), ocean floor, and island crystal rocks (Hansteen and Troll, 2003; Eiler et al., 2000).
Puis, aux stades inter mediaires, la formation de plagioclases reduit considerablement la teneur en Sr et, aux stades finaux, la formation de feldspaths alcalins en extrait le Ba et le Rb alors que se forment les trachytes et les phonolites a partir de magmas alcalins.
A second occurrence was reported from the Aris phonolite, Windhoek, Namibia (von Knorring et al., 1992).
The name tinguaite is applied to a dark green intrusive phonolite composed essentially of alkali feldspar, nepheline and aegirine, and characterized by the so-called "tinguaitic" texture.