The crystallization of the teschenite from the Lugar Sill, Ayrshire

Abstract

SUMMARY Twelve stages in the crystallization of the teschenite are defined by the commencement or cessation of crystallization of particular minerals. Ocellar structures, outlined by tangentially arranged biotite flakes, developed in liquid pockets after the sill had begun to consolidate, due to the coalescence of crystalline masses. It is thought that these ocellar structures were formed by the growth of gas bubbles and that this caused the expansion and fracturing of the partially consolidated sill. It is argued that the separation of the gas phase was the result of a retrograde increase in the vapour pressure during crystallization.