The mounds are amygdaloidal
in cross section, 11-20 mm long, up to 9 mm high and only slightly wider than the even ridge.
Hematite is found in amygdaloidal
cavities as druses of silvery black microscopic crystals on datolite, prehnite, albite, calcite, heulandite and stilbite.
The volcanics are amygdaloidal
in nature and exhibit porphyritic, cumulophyric and intergranular textures.
Some mineralization also occurs in the basalt above this horizon, in veins that transect the flows and in vertically bulging, dome-like regions of amygdaloidal
basalt, referred to as diapirs by Laskowich and Puffer (1990).
While the overlying aa makes excellent building stone, the pahoehoe beneath it is unsuitable for building because it is too soft, amygdaloidal
, and full of mineralized vesicles.
and porphyritic basalts occur in the northeastern and central regions of the study area.
The amethyst crystals occur in small to large clefts, or cleft-systems, which are similar to Alpine clefts and fundamentally different from geodes or amygdaloidal
cavities which are the result of gas bubbles in lava.
The UFU, of minimum 100 m thickness, is again dominated by massive, columnar-jointed, medium-grained basalt containing <20-30% mesostasis, and with minor amygdaloidal
zones containing zeolite minerals.
Most basalt in the area is massive, but considerable amounts are amygdaloidal
. Zeolites at Wasson Bluff commonly occur in basalt, conglomerate with basalt clasts, and less commonly in sandstone, but on average make up no more than 3% of the overall rock.
The upper 5 to 8 meters of this first flow is amygdaloidal
and contains the majority of the best specimen-quality minerals.
The Eastport Formation in New Brunswick comprises amygdaloidal
mafic flows and agglomerate, massive to flow-banded felsic flows, welded and non-welded lapilli tuff, pisolitic tuff, peperitic breccia, and grey to maroon sandstone and conglomerate totalling ~4000 m (Hay 1967; Pickerill and Pajari 1976; Pickerill et al.