Mineral Properties

Each type of mineral has its own combination of properties that identify it.

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 is the color of the powder that rubs off a mineral. This can be seen by rubbing a sample on an unglazed ceramic plate. Sometimes a mineral’s streak is very different from the color of the sample.

Hardness is the resistance of a mineral to scratching. Geologists use the Mohs' hardness scale to seriate and compare mineral hardness.

Specific gravity is the ratio of the weight of a volume of a mineral to the weight of an equal volume of water. Higher specific gravity means the mineral is heavier.

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 is how a mineral breaks when no cleavage surfaces form. For example, quartz breaks in a pattern known as conchoidal fracture (smooth, curved surface).

Luster is how a mineral reflects light or shines (glassy, vitreous, metallic, dull, and pearly).

Crystal - There are seven main geometric shapes of crystals - cubic, hexagonal, and tetrahedral.

Transparency describes how a mineral transmits light. transparent (see through them); Translucent (some light passes through) or Opaque (no light passes through).

Magnetism - some minerals (magnetite) are attracted by a magnet. Lodestone is a form of magnetite that is a magnet.

Reaction to acid - Calcite 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. Fluids such as molten rock, (below the Earth’s surface (magma) or at the Earth's surface (lava). Most of the quartz and feldspar is made this way. The fluids might be hot water (hydrothermal solutions) that have dissolved elements, like copper and gold, that flow through cracks in rocks. Other minerals, such as calcite and halite, often form from seawater, either through chemical reaction, deposition, or evaporation.

Dr. Robert Sweetland's Notes ©