Properties of Minerals The properties of a mineral depend on its composition and structure.

Same mineral in various colors and cuts. Minerals often occur in more than one color. Therefore, color by itself is not useful in identifying a mineral. The colors are caused by small amounts of different elements. Essentially, contaminants in the crystal form of the mineral. Same mineral in various colors and cuts.

Streak When minerals are scratched across a piece of unglazed porcelain, they leave a mark on the porcelain. The mark is called a “streak” and it represents the color of the mineral in its powder form. The color of the streak is very indicative of the mineral and different colors of the same mineral will give the same streak color.

Luster Luster refers to how light is reflected by the mineral. Luster can be metallic or nonmetallic. The types of nonmetallic luster are vitreous (glassy), pearly, silky, brilliant, and earthy.

Crystal Form Crystal form is the visible expression of the internal arrangement of atoms. In other words, the shape of the mineral on the outside reflects the positioning of atoms on the inside. The longer a mineral takes to cool, the better the crystals will be formed and the more obvious the shape.

Hardness The hardness of a mineral is determined using a scale called “Mohs scale”. Minerals are scratched with substances of various hardness to determine where they fit within the scale. For ex., Calcite is a “3” so it can scratch a fingernail (2.5) but a copper penny will scratch it (3.5).

Cleavage Cleavage is the tendency of a mineral to break (cleave) along flat, even surfaces. A mineral breaks in a certain pattern based on which bonds within the crystal form are the weakest. Mica cleaves in one direction and forms thin sheets.

Fracture If a mineral doesn’t cleave, then it fractures. Fracture means the mineral breaks unevenly. Minerals that fracture may break like glass, splinter, or form fibers. Many minerals show fracture.

Density Density is a unique value to a pure mineral so it is a great way to identify a sample (if it is pure). Density is determined by measuring the mass of the substance divided by its volume. Pyrite (fool’s gold) and real gold have different densities.

Distinctive Properties Some other properties that can be used to identify minerals are: how they feel, if they are magnetic, if they are see through and create double refraction, smell, or reaction with acid to form carbon dioxide. The properties of a mineral depends on its composition and structure.