Minerals: From the Inside Out • Minerals are the building blocks that make up rocks • There are about 2400 known minerals.
Answer These Questions • To be a mineral, all of the following questions must be answered “yes”: • Is it nonliving material? A mineral is inorganic. • Is it formed in nature? Only naturally made crystals are classified as minerals. • Does it have a crystalline structure (repeating inner structure that determines shape)? • Is it a solid? No gases or liquids allowed.
Two Groups of Minerals • Minerals are divided into two groups based on chemical makeup: • Silicate minerals – contain silicon & oxygen, with additional elements; make up more than 90% of Earth’s crust. • Nonsilicate minerals - no silicon or oxygen but C, O, Fe, S (carbonates – calcite, halides – fluorite, oxides – corundum, sulfates - gypsum
Silicate Minerals Quartz Feldspar Mica All silicate minerals contain the elements silicon and oxygen.
Nonsilicate Minerals CALCITE FLUORITE
Nonsilicate Minerals CORUNDUM GYPSUM
Identifying Minerals • Color • Impurities can change color (quartz vs. amethyst) • Air and water can also change color of mineral (pyrite is golden, but exposure turns it black)
Color Quartz and amethyst are both silicon dioxide (SiO₂) but amethyst contains impurities which gives it its purple color.
Identifying Minerals (cont.) • Luster • How the surface of a mineral reflects light. • Controlled by how atoms are bonded • Metallic, submetallic, nonmetallic (vitreous, silky, resinous, waxy, pearly, earthy)
Identifying Minerals (cont.) • Streak • Color of mineral in powdered form • Not always the same as color of mineral sample • More reliable than color of mineral Hematite may vary in color but the streak will always be reddish brown.
Identifying Minerals (cont.) • Cleavage and Fracture • How mineral breaks, determined by atomic arrangement • Cleavage – tendency to break along flat surfaces (mica, halite) because bonding is weakest in those directions. • Fracture – tendency to break along curved or irregular surfaces (quartz – conchoidal) when bonding is equally strong in all directions.
Identifying Minerals (cont.) • Hardness • Resistance to being scratched • Mohs hardness scale: Talc, Gypsum, Calcite, Fluorite, Apatite, Orthoclase, Quartz, Topaz, Corundum, Diamond
Scratch Test • < 2.5 = Mineral marks paper • 2.5 = Fingernail • 3 = Copper Penny • 5 = Steel knife blade • 6 = Plate of glass • 6.5 = Steel file
Identifying Minerals (cont.) • Density • How much matter there is in a given amount of space (D = m/v) (g/ cm³)
Identifying Minerals (cont.) • Special Properties • Fluorescence (calcite, fluorite glow under UV) • Chemical reactions (calcite) • Optical – calcite causes double images • Taste – halite • Magnetism – magnetic, pyrrhotite attract iron • Radioactivity – minerals containing radium or uranium can be detected with a Geiger counter.