Rock (geology)
In geology, a rock is a naturally occurring solid aggregate of one or more minerals or mineraloids. For example, the common rock, granite, is a combination of the quartz, feldspar and biotite minerals. The Earth's outer solid layer, the lithosphere, is made of rock.
Rocks have been used by mankind through out history. From the Stone Age rocks have been used for tools. The minerals and metals we find in rocks have been essential to human civilization.
Three major groups of rocks are defined: igneous, sedimentary, and metamorphic. The scientific study of rocks is called petrology, which is an essential component of geology.
Read more about Rock (geology): Rock Classification, Human Use
Famous quotes containing the word rock:
“When we were at school we were taught to sing the songs of the Europeans. How many of us were taught the songs of the Wanyamwezi or of the Wahehe? Many of us have learnt to dance the rumba, or the cha cha, to rock and roll and to twist and even to dance the waltz and foxtrot. But how many of us can dance, or have even heard of the gombe sugu, the mangala, nyang’umumi, kiduo, or lele mama?”
—Julius K. Nyerere (b. 1922)