What are rocks?

Rocks are simply aggregates of mineral grains. Each rock is unique as the composition of a rock varies from specimen to specimen. Understanding rocks is crucial to understanding the make up of the earth. Rocks are economically vital, and the minerals extracted from them are used in every aspect of our lives.

Classification/Types of rocks

Rocks are classified according to how they are formed.The main classes are:

Igneous rocks:

Which crystallise or form from a molten state. Eg, Granite, basalt, obsidian.

Sedimentary rocks:

Made up of fragments of reworked rocks, biogenic material or chemicals which precipitate on or near the earth’s surface. Eg, sandstone, limestone, mudstone, coal.

Metamorphic rocks:

Formed by heat and or pressure changing pre-existing rocks but without melting them. Eg, marble, schist, gneiss.

Rocks are made up of one or more minerals. Those with only one mineral are called mono-mineralic rocks. An example of this would be pure limestone. Most contain more than two minerals and are further classified on the basis of grain size, grain relationships, amounts and proportions of minerals and rock fabric.

If you require a rock to be identified, please contact us.

Queensland Museum's Find out about... is proudly supported by the Thyne Reid Foundation and the Tim Fairfax Family Foundation.