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
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
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 %).