How to Identify Granite Rocks

Yosemite National Park's El Capitan—a granite monolith

You probably don’t know how often you’re looking at granite. Resistant to erosion and durable, it is often used for monuments and buildings.Granite rocks are part of the igneous rock class, formed by slowly cooling pockets of magma trapped beneath the earth's surface. So how can you tell if you’re looking at granite?

Instructions

1. Inspect the rock closely. Granite has large, tightly fitted crystalline grains. Classic granite has a “salt and pepper” appearance, with grains of black and white.

2. Look for quartz in the rock. Granite always consists of quartz and feldspar, which usually give granite a light, almost glittery color, ranging from almost translucent white (from the quartz) to a pale pink (from the feldspar). This lighter color is mixed with grains of other darker minerals, creating the “salt and pepper” look.

3. Look at the fracture pattern. Because of its crystalline structure, granite naturally fractures in planes, resulting in a rough chunky shape. Gradual erosion by water and ice bevels this into smoothness, as characterized by the Granite Domes of Yosemite National Park.

Resources

• How to identify igneous rocks
• Be a rock hound