Amygdaloid

Amygdaloid (from the Greek amugdalos, an almond) a geological term applied to lavas in which bubbles of gas, escaping from near the surface of the stream, have left cavities which have been drawn out into an elliptical form in the direction of the flow of the viscous mass, and after the consolidation of the rock have been filled in by percolation with mineral matter. The minerals thus filling up the cavities are termed amygdules, as, being often calcite or some other light-coloured. substance, they resemble almonds in almond-toffee. The zeolite group commonly occur as amygdules.