The unmetamorphosed NE-SW oriented Sigula intrusion in North Estonia consists of medium-grained gabbro-monzonitic rock with
ophitic texture and of massive structure.
8.9 vs 11.4), texture and some details of mineralogy (e.g., Unit G is oniy slightly porphyritic and has analcite and
ophitic augite, which A does not).
The quartz occurrences are all related to basic volcanic rocks known as ophites, a general term for diabases that have retained their
ophitic texture (i.e.
The rock exhibits well-developed
ophitic texture where pyroxene encloses thin laths of plagioclase.
Their texture is coarse- to medium-grained, porphyritic to
ophitic and subophitic, with a doleritic matrix.
The rocks are typically fine to medium grained with hypidiomorphic granular to locally
ophitic texture involving amphibole and plagioclase (Fig.
Clinopyroxene (titanian augite, upper left) is
ophitic in habit.
3), and consist principally of fine-grained plagioclase laths and biotite with varying quantities of generally rounded and resorbed xenocrysts of K-feldspar and quartz; textures include doleritic,
ophitic, and microgranular (Fig.
The basaltic rocks are generally fine-grained and porphyritic, with sub-ophitic to
ophitic clinopyroxene, while the intersertal glass is charged with ore due possibly to devitrification.
Titanite ocelli (referred to as sphene-centered ocelli by Hibbard 1995) consist of titanite in
ophitic intergrowth with plagioclase, surrounded by a felsic zone consisting of K-feldspar + quartz + plagioclasc.
The significance of flow structure in microporphyritic
ophitic basalts of Arthurs Seat.
Petrographically the basalts are medium- to fine-grained with
ophitic textures and are variably vitrophyric ([less than or equal to]30 %).