Currently one of its popular products which is on point with the trend is the Andesine
The dioritic rocks are characterized by zoned plagioclase of andesine
composition in a sub-ophitic relationship with augite (Fig.
The low concentration of soluble [K.sub.2]O present in the phonolite may be due to the predominance of some constituent minerals such as: microcline (KAI[Si.sub.3][O.sub.8]), orthoclase (KAI[Si.sub.3][O.sub.8]), andesine
[(Na,Ca)[(Si,Al).sub.4][O.sub.8]] and e nepheline [(Na, K) AlSi[O.sub.4]] (Teixeira et al., 2012), where K is retained by covalent bonds in the crystalline network of the mineral, presenting low K release to the soil solution (Martins et al., 2008).
The plagioclase is commonly zoned, at places oscillatory, with much altered cores containing white mica and zoisite granules, and ranges from sodic andesine
Euhedral to subhedral plagioclase (andesine
) phenocrysts are often markedly zoned and show polysynthetic twining according to albite or pericline laws.
Plagioclase (0.8-4.0 mm), displaying andesine
core compositions ([An.sub.31-40]; Table 2 in Appendix A, and Fig.
Plagioclases in trachyandesites are characterized by andesine
to labradorite composition (37 to 65% An, Table 1).
The plagioclase (andesine
) porphyroclasts are fractured and some are split into several individual grains, which are separated by fine-grained recrystallized matrix (Fig.
The porphyrites of the Ilfeld Basin have plagioclase (oligoclase and andesine
), and in some cases spessartine, as phenocrysts in a dark, fine-grained groundmass similar to that of the melanophyres (Luedecke, 1896).
The plagioclase microlites range in composition from andesine
([An.sub.40]) to labradorite ([An.sub.58]) as determined from electron microprobe analysis.
Generally, they are composed of andesine
, hornblende, occasional biotite, with minor amounts of titanomagnetite, chromomagnetite and ilmenite.
Plagioclase is often replaced by alkali feldspar and varies in composition from andesine