Crystals are found as a rarity in the amygdaloidal cavities of igneous rocks.
This consists largely of rocks of igneous origin, of which the amygdaloidal diabase of Klipriversberg forms the type.
Of boulder beds and amygdaloidal lavas belonging to the Vaal River System.
The copper of the Lake Superior region is in the Keweenawaii system, chiefly in its sedimentary and amygdaloidal parts.
The Old Man presents a characteristic section, for it exhibits a thick pile of massive, current-bedded red sandstones, resting, near the foot of the pinnacle, upon a thin bed of amygdaloidal porphyrite, which in its turn lies unconformably upon steeply inclined flagstones.
Near Haco's Ness in Shapinsay there is a small exposure of amygdaloidal diabase which is of course older than that in Hoy.
These plateaus are composed of nearly horizontal sheets of basalt - columnar, amorphous or amygdaloidal - which, in Ben More, in Mull, attain a thickness of more than 3000 ft.
The axis along which they have been elevated runs north-east and south-west, and on either flank a series of " green rocks " appears, consisting of altered amygdaloidal andesitic lavas, intrusive dolerites, coarse gabbros and diorites, and at Beagh-beg and Creggan in central Tyrone ancient rhyolitic tuffs.
It occurs in a series of amygdaloidal dolerites or diabases, and in the associated sandstones and conglomerates.