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.