Mineral Identification Mr. Jensen Ref: McGuire – ES/PS

Identifying Minerals Minerals can be identified using their distinctive physical and chemical properties. Mineral properties include: –Color –Luster –Hardness –Cleavage –Streak –Characteristics –Composition

Table 2-1: Common Rock Forming Minerals

Minerals: Color Color –Many minerals have a characteristic color –Impurities may discolor certain light colored minerals Ex. Quartz and calcite which are typically colorless. –Dark color minerals typically do not have this problem.

Minerals: Luster Luster –Describes the way light is reflected from the freshly cut surface of a mineral. –Metallic Luster Hard shiny look like polished metal. Light is unable to penetrate. Ex. Pyrite, galena and magnetite –Non-Metallic Luster May be shiny but some light is able to penetrate. Includes glassy, waxy, pearly and earthy (dull) lusters Ex. Calcite, quartz and feldspar

Minerals: Streak Streak –The color of the mineral in a powder form. –The test for streak is performed by rubbing a fresh corner of the mineral across a white, unglazed streak plate. –Several minerals have a streak that is not the same color as the mineral itself. Most metallic luster minerals have a dark colored streak. (Ex. Graphite, Pyrite)

Minerals: Crystal Structure Crystal Structure –Minerals form characteristically shaped crystals –A crystal is a regularly shaped solid formed by an ordered pattern of atoms.

Minerals: Hardness Hardness –Minerals differ in hardness –Tested by scratching mineral with other materials of known hardness –Friedrich Mohs (Geologist) created the Moh’s scale for hardness

Minerals: Cleavage Cleavage cleavage –If a mineral breaks readily along flat surfaces it shows cleavage cleavage planes –Many minerals break along flat surfaces called cleavage planes fracture –Minerals that break along even surfaces that do not follow atomic arrangement (crystal faces) are said to show fracture

Minerals: Density Density –Minerals vary in density and specific gravity (ratio of density and water)