Phonolite, sometimes known as Clinkstone, is an igneous, volcanic (extrusive) rock, of intermediate (between felsic and mafic) composition, with aphanitic to porphyritic texture. Mineral assemblage is usually abundant feldspathoids and alkali feldspar, and lesser plagioclase, as illustrated by the position of the field for phonolite in the QAPF diagram. Biotite, amphibole and pyroxene are common accessory minerals. Quartz is absent, because alkalis are enriched relative to silica, as illustrated by the position of phonolite in the TAS classification.
Phonolite is a fine-grained equivalent of nepheline syenite, and the genesis of such magmas is discussed in the treatment of that rock type. ...
... Located in a region composed primarily of sedimentary rock, the tower was caused by hot, liquid magma slowly pushing its way through the layers of sediment toward the surface of the earth (as opposed to erupting, like from a volcano). The magma then cooled and solidified into a type of rock called phonolite, or clinkstone, containing large crystal formations. ...
... CLINK'STONE, n. [clink and stone, from its sonorousness. See Phonolite.]
A mineral which has a slaty structure, and is generally divisible into tabular masses, usually thick, sometimes thin like those of argillite. The cross fracture is commonly splintery. Its colors are dark greenish gray, yellowish, bluish, or ash gray; and it is usually translucent at the edges, sometimes opake. It occurs in extensive masses, often composed of columnar or tabular distinct concretions, more or less regular. It is usually found among secondary rocks; sometimes resting on basalt, and covered by greenstone. – Cleaveland. ...
Webster's Revised Unabridged Dictionary
n Phonolite (Min) A compact, feldspathic, igneous rock containing nephelite, haüynite, etc. Thin slabs give a ringing sound when struck; -- called also clinkstone.
... "Volcanoes: Past and Present" by Edward Hull
CLINKSTONE, called also phonolite, a felspathic rock of the trap family, usually fissile.
"Principles of Geology" by Charles Lyell ...
Phonolite, any member of a group of extrusive igneous rocks (lavas) that are rich in nepheline and potash feldspar. The typical phonolite is a fine-grained, compact igneous rock that splits into thin, tough plates which make a ringing sound when struck by a hammer, hence the rock’s name.
The most important constituent of phonolite is alkali feldspar, either sanidine or anorthoclase, which forms not only the bulk of the groundmass (matrix) but most of the large crystals (phenocrysts) in porphyritic varieties. Nepheline rarely appears in large crystals but may occur either interstitially or in well-formed microphenocrysts. The principal dark-coloured mineral is pyroxene: aegirine or titaniferous augite. Pyroxene phenocrysts occur as well-formed crystals; in the groundmass, pyroxene occurs characteristically as slender needles, often abundant enough to colour the rock green. An alkaline amphibole nearly always occurs as phenocrysts; barkevikite, riebeckite, or arfvedsonite are typical. Feldspathoids other than nepheline may be present as accessory minerals; the most common are nosean, sodalite, and leucite. ...
Phonolite is an uncommon extrusive rock, of intermediate chemical composition between felsic and mafic, with texture ranging from aphanitic (fine-grain) to porphyritic (mixed fine- and coarse-grain). Its intrusive equivalent is nepheline syenite.
The name phonolite comes from the Ancient Greek meaning "sounding stone" because of the metallic sound it produces if an unfractured plate is hit; hence the English name clinkstone.
Unusually, phonolite forms from magma with a relatively low silica content, generated by low degrees of partial melting (less than 10%) of highly aluminous rocks of the lower crust such as tonalite, monzonite and metamorphic rocks. Melting of such rocks to a very low degree promotes the liberation of aluminium, potassium, sodium and calcium by melting of feldspar, with some involvement of mafic minerals. Because the rock is silica-undersaturated, it has no quartz or other silica crystals, and is dominated by low-silica feldspathoid minerals more than feldspar minerals. ...