The rocks comprise feldspathoid
(silica undersaturated) bearing gabbros, diorites, monzonites and syenites which have unusual geological names such as meltegites, ijolites, unites and nepheline syenites.
(Web2) FGH afghanite a hydrous hexagonal feldspathoid
mineral of the cancrinite group.
Although microcline and calcium feldspar were feldspathoid
and contained the same crystal morphology, the material transformation resulted in changes to the macromechanical properties of the sandstone.
A linear K release over the period of 1 year was observed for the feldspathoid
nepheline at pH 5, with reduced K release at pH 7.
Frost and Frost (2008) devised a means of classifying alkaline igneous rocks and comparing their geochemistry with "normal" granitic rocks based a plot of alkalinity index (AI) versus feldspathoid
silica saturation index (FSSI) (refer to Fig.
Group 2 comprises quartz syenites, alkali quartz syenites, syenites (315 [+ or -] 15 Ma), feldspathoid
syenite, and ijolite (297 [+ or -] 4 Ma; ), carbonatite, lamprophyre, and associated pegmatite and fenites.
Topaz is a silicate mineral most often found in igneous rocks of felsic (relating to an igneous rock that contains a group of light-colored silicate minerals, including feldspar, feldspathoid
, quartz, and muscovite) composition.
Both the studied rock samples are porphyritic, with a small amount of phenocrysts formed by ferrifassaite passing to sodic ferrifassaite with kaersutite rims, oligoclase-andesine, and minor zeolitized feldspathoid
. Andesine to oligoclase ([An.sub.27-30]) predominate over sodic sanidine and scarce clinopyroxene and titanomagnetite in the matrix of fresh trachyandesite facies.
In its thin sections, the rock has a hypo-crystalline matrix which is composed of porphyritic texture and is rich in a sprinkled opaque mineral, plagioclase, feldspathoid
mineral and obsidian.
The change from incompatible to compatible behavior heralds the onset of significant plagioclase (or feldspathoid
It is a partially decomposed granite feldspathoid
having a greater diversity of alkaloids causing it to go into a gradual melt with less surface tension than true feldspars.
Afghanite [[(Na,Ca,K).sub.8][(Si,Al).sub.12][O.sub.24][(S[O.sub.4],Cl,C[O.s ub.3],[H.sub.2]O).sub.3]] is a feldspathoid
of the cancrinite group.