A
chilled margin is a shallow
intrusive or
volcanic rock texture characterised by a
glassy or fine grained zone along the margin where the
magma or
lava has contacted air, water, or particularly much cooler rock. This is caused by rapid crystallization of the melt near the contact with the surrounding low temperature environment. In an intrusive case, the crystallized chilled margin may decrease in size or disappear by later remelting during magma flow, depending on magma
heat flux.