Rock Topics

Texture (Part 3)

Pyroclastic rocks are composed of broken fragments and formed by volcanic eruptions.

Tuff, Mount Rogers Formation (Photograph by Parvinder Sethi)

MapRocks with pyroclastic  texture are made of broken fragments.  This rock, called tuff, consists of fine fragments created during a volcanic eruption.  Larger fragments are present in this sample from the Mount Rogers area of Grayson County.


Pegmatitic texture refers to intrusive igneous rocks called pegmatites with unusually large mineral grains.  Some individual grains can be several feet long.

(Photograph by Parvinder Sethi)

MapPegmatites have very large crystals.  This photograph shows a part of an Amelia County pegmatite on display at the National Museum of Natural History in Washington D.C.  Crystals in the pegmatite can be several feet long.