Minerals are inorganic substances, meaning that they do not come from an animal or plant. Yet animals and plants need minerals to live. Humans need the mineral calcium, for example, to develop healthy bones and teeth. Most plants get the minerals they need from the soil. Animals, including humans, get minerals from plants or from the milk, eggs, and meat of plant-eating animals.
Minerals make up the Earth's rocks and soils. They are also found underground because over time, rocks were broken down and covered by other soil. Minerals can have metallic or nonmetallic parts.
Mineralogy is the science that studies the physical and chemical properties of minerals. Mineralogists, or people who study minerals, have identified about 1,500 types of minerals.
Mineralogists use three main properties to identify an unknown mineral: color, hardness, and cleavage. Luster, or how the mineral reflects light, is one property that mineralogists use to determine a mineral's color. A mineral's hardness is usually stated in terms of the Mohs scale. The scale ranks ten typical minerals in terms of hardness, from the softest (talc), to the hardest (diamond). A mineral can be identified by comparing its hardness to the hardness of these ten minerals. The cleavage of a mineral is the way it splits or breaks. Mica, for example, breaks into thin, flat sheets. Mineralogists also use other properties, such as elasticity and strength, to identify minerals.
Rocks may be made up of one or more minerals. A combination of different minerals results in a different kind of rock. Rocks are classified into three groups—igneous, sedimentary, and metamorphic—based on how they were formed.
Igneous rocks were formed from the molten rock within the Earth. Granite is an igneous rock made up mostly of three minerals—quartz, feldspar, and mica.
Sedimentary rocks were made by clay or sand being compressed together. Sandstone and shale are the two most common sedimentary rocks. Quartz is the main mineral found in sandstone. Shale is composed mostly of kaolinite, with some quartz and mica.
Metamorphic rocks began as sedimentary or igneous rocks, but heat and pressure continued to change them. The most common metamorphic rock is gneiss. It is made up mostly of quartz and feldspar.
