Minerals Minerals Naturally occurring inorganic solids consisting of one or more chemical elements The atoms of these elements are arranged in a systematic internal pattern, which creates a a crystalline structure. Minerals are the building blocks of rocks Geologists spend a lot of time trying to determine which minerals are in rocks. Identifying what minerals are present is based on each minerals unique set of chemical and physical properties. Colour Not always reliable because colour can be changed by the presence of impurities in the mineral, by light, and by weathering of the mineral’s surface. Azurite is always blue, malachite is always green. Malachite Azurite Luster How the mineral’s surface reflects light (shiny, glassy, silky, pearly, etc.) Galena has a metallic luster Streak Color that is displayed when the mineral is rubbed across a streak plate (more reliable than just external color). Streak color will not always be the same as the color of the mineral. Galena streaks gray; Hematite streaks red. Specific Gravity A comparison of the weight of the mineral to the weight of an equal volume of water. For example, gold has a specific gravity of 19.3, which means that it weighs 19.3 times as much as an equal volume of water. Specific gravity can be used to distinguish gold from pyrite (Fool’s Gold) which has a specific gravity of only ~4. Hardness A mineral’s resistance to scratching Measured using Mohs Hardness Scale Mohs Hardness Scale Increasing Hardness Mineral Hardness Talc 1 Gypsum 2 Hardness of Some Common Objects Human fingernail (2.5) Calcite 3 Copper penny (3.5) Fluorite 4 Apatite 5 Glass (5-6) Pocketknife blade (5-6) Orthoclase (potassium feldspar) 6 Steel file (6.5) Quartz 7 Topaz 8 Corundum 9 Diamond 10 Cleavage The tendency to break consistently along distinct planes. Example, halite always forms cubes Fracture When minerals don’t cleave, they fracture – break at random spots Forms jagged, irregular surfaces. Smell and Taste Sulfur-containing minerals stink like rotten eggs Halite is salty tasting Effervescence Minerals containing carbonate, such as calcite, will fizz when mixed with dilute hydrochloric acid Crystalline Form The shape of the crystals the mineral forms.