The finest (< 5 [micro]m) groundmass
serves as a matrix for scattered grains > 5 [micro]m in size.
The [sup.40]Ar/[sup.39]Ar analysis of groundmass
plagioclase sample D1-1 was carried out at the Vrije Universiteit (VU) in Amsterdam using the VULKAAN [sup.40]Ar/[sup.39]Ar C[O.sub.2] laser probe and a MAP 215-50 double focusing noble gas mass spectrometer fitted with a Johnston MM1 secondary electron multiplier detector (Wijbrans et al.
The andesites of Noorabad ophiolite in hand specimen and thin section have phenocrysts of plagioclase in a groundmass
of clinopyroxene and amphibole minerals.
surrounding the glass clasts and crystal fragments seem to be flushed with organic matter with different sizes and structures showing different degrees of biodegradation and alteration to amorphous organic matter (AOM).
The hypocrystalline groundmass
contains clinopyroxene (39-46 vol%, Mg# ~0.75), olivine (3-6vol%, [Fo.sub.74-76] mole%), titanomagnetite (4-7vol%, up to 43% ulv.
Many of the river cobbles collected often had very irregular surfaces, where the phenocrysts jut out from the eroded groundmass
In addition to these visual observations, a powder x-ray diffraction analysis was run on one coprolite specimen to determine the major composition of its groundmass
The respective values for the groundmass
of the inside-crater crystalline-derived breccia matrix range from -27.30 [per thousand] to -28.35 [per thousand], and is -25.70 [per thousand] for the magnetic particles.
It is characterized by a wide range of very low-grade, low-grade, and rare medium-grade metamorphic rock fragments, set in a groundmass
rich in mica laths and quartz grains.
Despite the inclusion of statements such as 'all contain sanidine in the groundmass
as well as significant amounts of plagioclase ...