Question - Explain the difference between porphyritic and pegmatitic textures.

Explain the difference between porphyritic and pegmatitic textures.

ANSWER:

In porphyritic rocks there are two distinct crystal sizes that are indicative of two stages of cooling (slow then fast). The fine material can range from glass to several mm, as long as the coarse crystals are distinctively larger. In pegmatitic rocks the crystals are consistently coarser than 1 cm, and can be much larger. Pegmatites form the slow cooling of water-rich magmas.