objective: 3240-0503

WHAT IS A ROCK?
At first this seems like an easy question. We see rocks every day. But have you ever thought about them (besides when you stub your toe) ? Each rock is like reading a story. By studying them we can learn about how the earth's crust is formed.

A rock is a mixture of one or more minerals, glass, and sometimes, organic matter (something that was once living). Some rocks are shiny, some are flat and dull, others are very compact. Analyzing these differences can help us understand how they were formed.

CLASSIFYING ROCKS
We can also use the characteristics of rocks to classify them. Geologists separate rocks into three main categories based on how they were formed: igneous, metamorphic and sedimentary.