The grain sizes of dikes range from microscopic to several tens of centimeters. In one pegmatite dike near Madawaska, north of Bancroft, which was mined for feldspar, a single crystal measuring 7 meters long and weighing 300 tons was extracted. These are all found in cross-cutting dikes that are clearly intrusive. Porphyries pose another serious problem for Gentry's interpretation. Geologists can easily explain them.
Different minerals melt at different temperatures.
So, as a magma chamber cools the minerals with the highest melting point crystallize first. Igneous rocks come in a variety of grain sizes and the principle factor that controls grain size is the cooling rate - slow cooling results in large crystals, fast cooling results in small crystals, and very rapid cooling results in glass. This has been known to geologists and chemists for at least 150 years and can be readily demonstrated in the laboratory. Gentry is simply wrong in his conclusions about the importance of grain size.