Rock-forming minerals
Alkali feldspars
Alkali feldspars are abundant in all samples. They occur as phenocrysts, medium sized
crystals and in groundmass grains. The chemical composition of alkali feldspars is
characteristic of all studied fonolitic – trachytic rocks (fig. felcumul). Most abundant are
sanidine, Na-sanidine and anorthoclase with a higher content of An-component.(3 to 5 mol.%
of An). K- feldspar (probably orthoclase) is less frequent as much as albite and the content,
fewer of anorthite component, represents lower temperature of origin.
The sodalithic phonolite contents predominatly Na-sanidine, anorthoclase and albite.
Plagioklase is present only in some sodalithic phonolite and is represented by oligoclase,
andesine (in part K-andesine) and labradorite. Labradorite is evidently component of
(micro)xenoliths. Celsian component in alkali feldspar is most abundant in Na-sanidine and
anorthoclase ( Ab41), at the same time rich in An-component (about An04) and consequently
put together with the high temperature origin.
In phonolite s. s. were catched only alkalic feldspars, overmore poor in Ancomponent, therefore of the low-temperature provenience.
The feldspar of tinguaite is characterized by the absence of end members of alkali
feldspars series and relatively rich in distribution of K-oligoclase fluently continuating to
anorthoclase. Presence of An-component rich anorthoclase and K-oligoclase confirms hightemperature origin of the feldspars that is typical of most studied rocks.
The feldspar of alkalic trachyte is characterized by occurrence of large amout of Kandesine with transition to anorthoclase, Na-sanidine and sanidine. Sodalithic trachyte
contents similar feldspar as alkalic trachyte with exception of presence of albite.
Representant of feldspar of trachyandesite is albite and Na-sanidine on one hand and
oligoclase and andesine on other hand.
Plagioclase
Plagioclase is rarer in studied rock then alkali feldspar and occurs more in groundmass then in
phenocrysts. The chemical composition of plagioclase results from fig. felcumul and table
[tabulka minerálů]. K-oligoclase is characteristic of phonolite, while K-andesine is
representative of trachyte and trachyandesite. Ba rich plagioclase (3% Cn-component) is Kalbite to K-oligoclase (An8-10 Or25-21). Presence of labradorite corresponds with occurrence of
molten xenoliths.
Barium rich feldspars were noted mainly in alkali trachyte, where Cn-componet content
achieves 16% in Na-sanidine or sanidine. In sodalitic phonolite and sodalitic trachyte they
occur too. In K-oligoclase of sodalitic trachyte highest content of Cn-component were
registered (2%).