39]Ar analysis of groundmass
plagioclase sample D1-1 was carried out at the Vrije Universiteit (VU) in Amsterdam using the VULKAAN [sup.
3, bottom), the groundmass
was relatively dense, with sub-horizontal and sub-vertical thin planes, and some irregular to rounded small voids.
Quartz phenocrysts in the rock are relatively large and surrounded by grey-brown sub-microscopic groundmass
Redeposited material is distinguished by the lack of parallel orientation and lamination of deposits, with the inclusions being embedded in a mixed ash and organic rich groundmass
Microprobe analysis of the yellow organic groundmass
indicates a higher clay content than in the black organic materials.
1 millimetre and less), light greyish yellow or bluish grey groundmass
is granophyric, partly spherulitic, and contains miarolitic cavities.
Hornblende occurs in some of the dikes as small needles in the groundmass
or as large ragged grains.
Disseminated arsenopyrite and pyrite occurs in the groundmass
of the porphyry and is related to the fracturing and subsequent alteration.
is commonly overprinted by secondary phases and in a few localities, all primary features have been obscured.
At these three sites, the upper part of the lower unit represents a buried surface horizon, containing euhedral sparitic calcite crystals in the groundmass
and in pores (Mees and Van Ranst 2011).
The primary mineralogy of komatiites is simple: phenocrysts of olivine and spinel/chromite (+/pyroxene) are enclosed in a groundmass
composed of glass, calcic clinopyroxene and minor orthopyroxene.