Rocks, Minerals & Gem Identification

Minerals are naturally occurring inorganic substances that have a specific properties, and they can be identified by testing each property. A gem is a precious mineral used in jewelry. Rocks are a mixture of more than one mineral. Some of the properties used to identify minerals and rocks are hardness, luster and texture.

Thin slice of a rock for identification

Hardness

Hardness is the resistance of a mineral to being scratched. Minerals and gems are scratched with various instruments, such as glass plates or a steel file, to determine their hardness on a scale of 1 to 10, called the Mohs scale; 1 is the most easily scratched, and 10 is the least easily scratched.

Streak

Streak is the color of the powder of a mineral. It is tested by rubbing the mineral or gem against a unglazed porcelain tile. The color left on the tile is used in identifying the mineral or gem.

Luster

Luster is the way a mineral or gem reflects light. There are two types of luster: metallic and non-metallic. Metallic minerals are shiny and opaque. Non-metallic minerals may be glassy, dull or resinous.

Texture

Rocks can be identified, in part, by their texture. Course grained, fine grained and glassy are different rock identifications.

Composition

Rocks are made up of specific mineral compositions. For example, pumice is made of silica, and scoria is made of iron. They look similar, but their compositions make them two different rocks.

References

• Rock Identification
• Mineral Identification Tests