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 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 – If a mineral breaks readily along flat surfaces it shows cleavage – Many minerals break along flat surfaces called cleavage planes – Minerals that break along even surfaces that 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)