Overall, the blocks show a hypocrystalline, porphyritic texture with plagioclase, clinopyroxene, orthopyroxene, and olivine phenocrysts
in an intersertal matrix (Figs.
Plagioclase (54%) forms heteroblastic and xenoblastic individuals, which constitute former phenocrysts
or matrix of the protolith.
2008); the presence of large potassium feldspar phenocrysts
indicates that the magma may have been sequestered in the deep crust for some time before rising and solidifying nearer to the surface (McLeod 1990).
One of these, a medium-grained gabbroid, contains up to 3 cm long phenocrysts
The samples were porphyric coarse-grained biotite granite with the occurrence of feldspar phenocrysts
up to 3 cm in size and directionless structure.
The dominant minerals are plagioclase phenocrysts
, quartz, K-feldspar, and hornblende and accessory minerals such as biotite, pyroxene, apatite, sphene, and opaque minerals can be seen in some of these rocks.
7) indicate fractional crystallization of mafic minerals and early fractionation of plagioclase, the latter being in agreement with the presence of plagioclase phenocrysts
5) are usually angular and show different textures, from fluidal with phenocrysts
of forsteritic olivine, to highly vesicular scoriaceous.
The hyalite-bearing layer is composed of 3-50 mm rhyolite rock fragments mixed with 1-4 mm dipyramidal fe-quartz and limpid sanidine phenocrysts
in a weakly welded, porous, siliceous, tuffaceous matrix.
New method of semi-automatic modal analyses for phenocrysts
of porphyritic rocks based on quantitative digital colour specification technique.
The andesites of Noorabad ophiolite in hand specimen and thin section have phenocrysts
of plagioclase in a groundmass of clinopyroxene and amphibole minerals.
Contained within the bentonites are remnant diagnostic mineral phenocrysts
that are unique to the composition of each volcanic ash deposit.