Minerals are the ingredients that make up rocks. Minerals may be composed of a single element, such as gold or copper. These are called native elements. Other minerals are made of compounds of elements. Quartz is a combination of the elements silicon and oxygen (SiO2).
Find out about mineral properties >>
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| Quartz | Feldspar |
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| Fluorite | Magnetite |
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| Hornblende | Gypsum |
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| Calcite | Biotite |
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| Copper | Hematite |
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| Pyrite | |
Mineral Properties
Each type of mineral has its own combination of properties that identify it. Some of the properties are
Color
Many minerals come in a wide variety of colors. Different minerals can be the same color. It is difficult to use just color to identify a mineral.
Streak
Streak is the color of a mineral in powdered form. You can see a mineral’s streak by rubbing a sample across an unglazed ceramic plate and observing the powder left behind. Sometimes a mineral’s streak is very different from the color of the sample.
Hardness
Hardness is the resistance of a mineral to scratching. Geologists use the Mohs' hardness scale to seriate and compare mineral hardness.
Specific gravity
Specific gravity is the ratio of the weight of a given volume of a mineral to the weight of an equal volume of water. Higher specific gravity means the mineral is heavier.
Cleavage
Cleavage is how a mineral breaks. Some minerals break in smooth, flat surfaces at identifiable angles, such as calcite. Others fracture and produce no flat surfaces, such as quartz.
Fracture
Fracture is how a mineral breaks when no cleavage surfaces form. For example, quartz breaks in a pattern known as conchoidal fracture. Conchoidal fracture looks like smooth, curved surfaces.
Luster
Luster is how a mineral reflects light or how it shines. Some ways to describe luster include glassy or vitreous, metallic, dull, and pearly.
Crystal form
Crystal form describes the geometric shape of a crystal. There are seven main groups of crystal shapes, including cubic, hexagonal, and tetrahedral.
Transparency
Transparency describes how a mineral transmits light. Some minerals are transparent (you can see through them); others are translucent (some light passes through a sample) or opaque (no light passes through a sample).
Magnetism
Magnetism is a special property of some minerals, especially magnetite. Samples are attracted by a magnet. Lodestone, a special form of magnetite, is a magnet itself.
Reaction to acid
Some minerals react to acid. Calcite especially will fizz and bubble when it comes in contact with an acid such as hydrochloric acid at room temperature.
Mineral Formation
Minerals form in fluids. The fluids could be molten rock, such as magma beneath Earth’s surface or lava at the surface. Quartz and feldspar form this way most of the time. The fluids might be hot water (hydrothermal solutions) that contain dissolved elements that are deposited in rocks. Copper, gold, and other native elements often form this way in bubbles and cracks in rocks through which the hot solutions moved. Other minerals, such as calcite and halite, often form from seawater, either through chemical reaction and deposition or by evaporation.
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