Multiple growth twinning of k-feldspar in hypersolvus granite

Multiple growth twinning, involving three or four sub-individuals, occurs sporadically in the K-feldspar (mesoperthite) of hypersolvus granites from Norway and South Australia. The twin lamellae resulted from perturbations during crystal growth, as opposed to the formation at the nucleation stage applicable to simple twins. The unusual conditions controlling the formation of the lamellar twins are presumably localized, but not understood, and could be related to bursts of increased supersaturation resulting from transient perturbations in cooling rate or loss of volatiles.