Based on investigations found that the Ambela alkali granite have two textural types; a) Megaporphyritic and b) Microporphyritic
. Both the textural types of Ambela granite have high specific gravity and low water absorption capacity however; the Megaporphyritic alkali granite has higher specific gravity and lower water absorption value.
The two summits of the hill defined by the Logrosan granite (the San Cristobal hill) are composed of a microporphyritic (two-texture) granite and an aplitic granite (Evolved Units) (Fig.
A total of 9 representative samples weighted between 3-5 kg were collected for whole-rock geochemistry (6 medium to coarse-grained granites from the Main Unit and 3 fine-grained or microporphyritic granites from the Evolved Units) (Table 1).
Investigation of nine representative thin sections leads to a further subdivision of the alkali granite into two textural types: (i) megaporphyritic and (ii) microporphyritic.
The irregularity displayed by the phenocryst shapes in quartz syenite is higher than that in both the megaporphyritic and microporphyritic types of the alkali granite but comparable to that in nepheline syenite, which is fine to medium grained.
These include: alkali granite, granite and microporphyritic
The rhyolite occurs as aphanitic to porphyritic flows and ignimbritic tuffs with flow banding and microporphyritic
to porphyritic textures (Fig.
The significance of flow structure in microporphyritic
ophitic basalts of Arthurs Seat.
Lavas are commonly amygdaloidal and/or microporphyritic with phenocrysts of feldspar and, more rarely, pyroxene or quartz, set in a glassy to microcrystalline groundmass.
Most of the samples are amygdaloidal and microporphyritic with glassy to microcrystalline groundmass.