2.3 – Properties of Minerals

Do Now What are the eight properties of minerals?

Do Now What are the eight properties of minerals? Color Streak Luster Crystal Form Hardness Cleavage Fracture Density

Key Words Tendency Distinctive Expression

Vocab Words Streak Luster Crystal Form Hardness Mohs Scale Cleavage Fracture Density

Minerals In order to properly identify minerals, we look at their characteristics and their properties to determine the identity of the mineral. Most minerals are easily identifiable, whereas others are not so that is why we look at the eight properties.

Color This is the property looking at the visible color of the mineral. One of the first things you will notice about a mineral is its color. Some minerals have a unique color, other will not; so this property is often not used in identifying minerals. Small amounts of different elements can give the same mineral different colors.

Streak This is the color of a mineral in its powdered form. Streak is obtained by rubbing the mineral across a streak plate (unglazed porcelain). The streak color may not always match the visible color of the mineral. Streak is a good indicator of mineral identification since it will also show the difference between metallic and nonmetallic luster in a given mineral. Metallic lusters – dark, dense streak Nonmetallic lusters – not dark or no streak

Luster Luster is described as how light reflects from the surface of a mineral. How shiny the mineral is. The mineral will have either a metallic luster or nonmetallic luster. Metallic – Have the appearance of metals Nonmetallic – May look glassy, but not like a shiny metal

Crystal Form The visible expression of a mineral’s internal arrangement of atoms. Every mineral has a distinct crystal form. When a mineral forms slowly and without space restrictions, it will develop into a crystal with well- formed faces – sides, top and bottom.

Hardness One of the most useful properties to identify a mineral is hardness. Hardness is the measure of the resistance of a mineral to being scratched. Geologists use a standard hardness scale called Mohs scale. The Mohs Scale consists of 10 minerals arranged from 10 (hardest) to 1 (softest) Any mineral of unknown hardness can be rubbed against these minerals to determine its hardness. Other materials can also be used, such as your fingernail, copper penny, etc.

Mohs Hardness Scale

Cleavage In the atomic structure of a mineral, some bonds are weaker than others. This is where a mineral will break when stressed. Cleavage is the tendency of a mineral to cleave, or break, along flat, even surfaces. Some minerals will cleave in more than one direction. Mica is the best example of cleavage in one direction. Minerals that do not have cleavage, will fracture instead.

Fracture Minerals that do not show cleavage when broken are said to fracture. Fracture is the uneven breakage of a mineral.

Density Density is a property of all matter that is the ratio of an object’s mass to its volume. Density = mass/volume

Other Distinctive Properties Some minerals can be recognized by other distinctive properties such as how they feel, magnetism, etc.

Group Challenge Question Your friend shows you a crystal that he thinks is a diamond. Without asking an expert, how could you tell if the crystal is really a diamond?