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rock \ n 1 : a mass of stony material also : broken pieces of stone 2: soild mineral deposits 3 : something like a rock in firmness 4 : Gem; esp : diamond - rock adj - rock-like adj - rocky adj

A rock, by definition is a naturally occurring mass of mineral matter that constitutes an essential part of the Earth's crust. Rocks are assemblages of two or more minerals. For example, the igneous rock granite is composed chiefly of the minerals mica, quartz, and feldspar. The sedimentary rock sandstone is made op primarily of the mineral quartz. The metamorphic rock gneiss is an assemblage of quartz, feldspar, and various dark minerals.

Rocks are one of the main sources of information for geologists. By comparing rocks and minerals and their locations, geologists can estimate approximately how old the rocks and minerals are. They can tell if a rock was formed on dry land, on an ocean floor, or deep inside the earth.

The main difference between rocks and minerals is that a mineral is homogeneous. This means, it is the same all the way through. if you look at a crystal of salt under a microscope, every part of it has the same structure. But rocks are not homogeneous, they are a mixture.

Rocks are organized into three categories depending on the way they are formed. These categories are sedimentary, igneous, and metamorphic.

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