Biotite is subidiomorphic
and alotriomorphic, reaching up to 5% of the mineral volume and, like the potassium feldspar, is intensely weathered which is responsible for the iron oxide cementing fissures.
Albite has been found in clusters of tabular crystals in parallel growths up to 4 cm and, less commonly, in isolated xenomorphic or subidiomorphic
crystals to several millimeter size.
At TEM scale, the aspect of these flakes is subidiomorphic
, with curled edges and fractures, sized < 1 [micro]m (Fig.
In some gneisses, and in the previously described schists, there are also small idiomorphic or subidiomorphic
7) and dark luminescence zircons forming either homogeneous subidiomorphic
grains or rims around detrital zircon cores (Fig.
5a), defined by large (up to 1.9 mm) subidiomorphic crystals of olivine replaced by secondary calcite, chlorite and opaque minerals, set in a finer-grained groundmass (150-250 [micro]m).
It shows a porphyritic to doleritic microstructure with subidiomorphic large crystals of olivine (up to 1.6 mm).
Olivine constitutes subidiomorphic
phenocrysts completely replaced by secondary assemblages including chlorite and opaque minerals.
Quartz grains are the most abundant fraction (27-33 %) and present two distinct types: rounded to subrounded (30-45%), with wavy extinction most of them, and angular, subidiomorphic
, with corrosion pockets and inclusions of mica, rutile and fluids (55-70%).