2) from Staric hard coal underground mine (approximately 15 km S from Ostrava) is predominantly composed of
subangular to angular monocrystalline quartz grains with average grain size ([M.sub.d]) of 0.36 mm.
The soil mineral coarse fraction had varied sizes and well-preserved edges (
subangular to subrounded), indicating low contribution of the sedimentary material to the soil formation.
The petrographic study reveals the fine to very coarse quartz grains along with
subangular to subrounded grain shape and poor sorting.
Transverse equatorial sections show elliptical,
subangular, triangular, and nearly circular endocarp outline (Fig.
Conchoidal features of various sizes (Figs 5, 6I), along with straight and arcuate steps (Figs 5, 6J) and parallel striations (Figs 5, 6K), occur on angular and sometimes on
subangular grains.
The dominant size for these
subangular quartz grains is 30-50 [micro]m (e.g.
It comprised various dimensions of
subangular siltstone gravels together with silty clay and clay; the gravel content was approximately 10~70% (Figure 2(a)).
Frequency (%) (a) Cobble 12.61 Pebble 70.54 Coarse sand 5.36 Medium-fine-sand 9.13 Silt mustone 2.36 (c) Frequency (%) Well sorted 1.92 Medium sorted 11.54 Poor sorted 86.54 (d) Frequency (%) Round 5.77 Round subrounded 69.23 Subrounded 8.65
Subangular subrounded 6.73
Subangular round 8.65 Angular 0.96 Note: Table made from bar graph.
(3) WE = weak; ST = strong; MO = moderate; VST = very strong; FI = fine; FM = fine and medium; VM = very fine to medium; MC = medium and coarse; ME = medium; CO = coarse; VC = very coarse; EC = extremely coarse; GR = granular; SB =
subangular blocky; AB = angular blocky; PR = prismatic.