EAS 112 Lab Section 2 (Spring 2003)

Lab II. Igneous and Metamorphic Rocks

The Rock Cycle

Igneous Rocks

I. Texture: refers to the size, shape, and arrangement of the crystals or grains composing the rock. It is a consequence of the physical and chemical conditions under which it formed and, perhaps, some of the processes that have acted on the rock since that time.

• Crystalline texture
• Glassy texture
• Aphanitic (/fine-grained) texture
• Porphyritic texture
• Pyroclastic texture

II. Major igneous rocks

• Granite and rhyolite (special example: granitic pegmatite)
• Gabbro and basalt
• Diorite and andesite
• Peridorite/Dunite
• Obsidian
• Pumice and Scoria

Metamorphic Rocks

I. Classification: subdivided into two main textural groups - nonfoliated and foliated. Foliation is the arrangement of mineral crystals in parallel or nearly parallel planes. Nonfoliated metamorphic rocks lack flat mineral crystals with parallel alignment, instead, crystals are all about the same size and are interlocked in a crystalline texture.

II. Major metamorphic rocks

Foliated

• Slate
• Schist
• Gneiss

Nonfoliated

• Marble
• Quartzite