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%).
Feldspathoids figure both in phenocrysts and in groundmass in various proportions.
The composition of nepheline, sodalite, hauene and nosean is presented in table xx. It is
present in phonolite, sodalitic phonolite, sodalitic trachyte, trachyandesite, andesitic trachyte
and tinguaite. Nepheline phenocrysts were mostly resorbed in the all studied rocks. The relics
were confirmed in porphyritic tinguaite, phonolite, sodalitic phonolite and trachyandesite,
whereas in other samples they were either totally analcimized or altered to a mixture of clays
and zeolites . The chemical composition of the nepheline plots both near the composition of
Si-poor nepheline and does not exceed the limit defining an excess of SiO2 in solid solution
in the Na-Ks-Qz-H2O systém at 700oC and 1kbarPH2O (fig. Xx) defined by Hamilton (1961)
(tinguaite), and nepheline of the other studied rocks ofen exceeds the limit defining the excess
of SiO2 (fig.xx). The composition variation of the Ks-component ranging from 10 to 20
mol.% is greater in phonolite and trachyandesite then in tinguaite. Nepheline phenocrysts are
weakly zonal with regard to distribution of K and Na. The rim uses to be rich in K but it is
not principal. Nepheline in the groundmass is generally rich in K and Ca..
Sodalite is abundant mineral and determinates some types of studied rocks. It occurs
as pristine grains of sodalitic phonolite and sodalitic trachyte. It was analyzed also in
phonolite and tinguaite (see tab. Xx.).
Hauyene is present in addition with sodalite also in alkali trachyte. Especially
abundant it is in phonolite s.s. (Loc. Varta). Nosean is frequent in tinguaite
Analcime occurs mostly in sodalitic phonolite andesitic trachyte, trachyandesite and
tinguaite. Analcime not only replaces nepheline but is also present in the interstices. Chemism
of analcime is illustratet in fig. Xx and tab. Xx.
Pyroxen
Diopside is most abundant in alkali trachyte and sodalitic trachyte. It occurs rarely in sodalitic
phonolite and trachyandesite. It stands out both in phenocrysts and matrix. In sodalitic
phonolite together with diopside exists augite and aegirineaugite. Hedenbergite occurs in
some sodalitic phonolite only (Jílové, Rytířov). Phonolite s.s. is characterized rather by
aegirinaugite to aegirine. In matrix of tinguaite sporadic aegirine occurs. Distribution of
pyroxen in the studied rocks is presented in fig. Xx and xx.
Amphibole
Most abundant amphibole is doubtless kaersutite. It occurs surprisingly in wide range of the
studied rock as sodalitic phonolite, tinguaite, sodalitic trachyte and trachyandesite. Further
amphiboles are hastigsite in trachyte, some tinguaite and arfvedsonite in alkali trachyte.
Together with kaersutite in sodalitic trachyte ferroan pargasite occurs. Series of amphiboles
in the studied rocks is completed by tschermakite and tschermakitic hornblende in the
phonolite s.s. Overview of amphiboles is apparent of fig. Xxx and xxx, and tab.xx.
Rich amphibole series is in tinguaite, where prevails over pyroxen. Ferroan-pargasite
represents it mainly . Rare ferro-pargasite, Fe-pargasitic hornblende and magnesia hastingsite
or hastingsite occur. Kaersutite forms entirely the cores of phenocrysts with ferroan-pargasite
rim (tab. Xx and fig. Xx.). Occurrence of magnesian hastingsite and hastingste is differed by
the locations (Skrytín and Roztoky).
Magnetite is most frequent accesory mineral of phonolite, sodalite phonolite and alkali
trachyte. It is present in groundmass or in lesser phenocrysts. The plot of magnetite in the
figure TiO2 – FeO – Fe2O3 (fig.xx) shows the most content of ulvospinel component (to 50
mol.%) in alkali trachyte. Lower content of ulvospinel component is in sodalitic phonolite
and the lowest one in phonolite (10 mol.%). Content of MnO fluctuates from 0.69 wt.% (in
phonolite) to 2.87 wt.% in sodalitic phonolite and 3.23 wt.% in alkali trachyte, but in sodalitic
trachyte fluctuates in large range from 1.5 wt.% to 4.5 wt.%. Tinguaite contains magnetite
with ulvospinel component from 5 mol.% to 24 mol.% (are not involved in the plot of
fig.xx.).
Sphene is frequent accessory mineral in sodalitic phonolite, sodalitic trachyte,
tinguaite and mainly in alkali trachyte. It occurs rarely fresh , mostly is in part decomposed. It
distinguishes itself by higher content of FeO (2.5 wt.%) then Al2O3 (1 wt.%).
Apatite is frequent accessory of phonolite, sodalitic phonolite, alkali trachyte and tinguaite.
Pure fluorapatite is present in phonolite s.s. In sodalitic phonolite and in alkali trachyte is
about 0.5 wt.% and 0.7 wt.% SO3. The tinguaite apatite is fluorapatite with less content of
SO3 then in sodalitic phonolite and alkali trachyte. It distinguishes itself by low content of Sr
and REE.