Please describe how, and explain why the texture of an igneous intrusion would change from the outer edge to the centre.

When intruding, hot magma contacts the cool country rock this will cause the outer edge will quickly cool and harden, therefore there will not be much time for crystals to form leaving a very fine crystal texture on the outer edge. However, the hardened outer edge then acts as an insulator for the inside of the intrusion. this causes the remainder of the intrusion to cool at a much slower rate and so allowing for crystals to form and become much larger towards the centre of the intrustion where the cooling is slowest meaning there will be a very obvious range from fine crystals to course crystals in the intrusion from outer edge to centre.