Lesson 1: Rock Identification

Key Idea

A rock’s appearance acts as a window into its past. By closely examining a rock's texture, one can identify the process that formed it.

Igneous rocks typically feature tightly interlocking crystals, a pattern created when molten liquid cools and freezes. In contrast, sedimentary rocks often look grainy or layered, revealing that they are composed of many smaller particles glued together. Identifying these distinct textures allows for the classification of rocks based on their origin.

Key Idea

Rocks originate from two very different natural processes. Igneous rock is born from extreme heat; it forms when magma (molten rock) cools down and hardens into a solid.

Sedimentary rock, however, is born from accumulated debris. Over time, layers of loose sediment (sand, mud, and pebbles) build up and harden into stone. Recognizing these two formation paths explains why the Earth’s crust is made of different types of materials.