Geology 101 Lab 2 Monday September 8 2014 Minerals The Building Blocks of Rocks Chapter 3 Importance of Minerals Minerals are the building blocks of the rocks that comprise the solid earth o They are the physical foundation of our planet AND our society Common metals such as aluminum copper and iron as well as precious metals such as gold and silver occur in the earth as mineral ores Other minerals that we commonly use include o Talc bath powders and cosmetics o Halite salt o Micas cosmetic powder o Graphite pencil lead o Gypsum drywall o Calcite antacid The mineral data base in lab manual lists more and common uses By Definition a Mineral Is Is a naturally occurring Is an inorganic Is a solid Has an ordered internal molecular structure a three dimensional arrangement of atoms A characteristic chemical composition Is It A Mineral Brick o No Man Made Coal o No Made of organic matter Diamond o Yes Granite o No made of many minerals Ice o Yes Oil o No liquid and organic Physical Properties The crystalline structure and unique chemical composition of minerals gives each of them a unique set of physical properties Physical properties are often used to identify minerals o Color often unreliable Ex quartz smokey quartz rose quartz citrine amethyst o Streak o Crystal Form o Luster o Hardness o Cleavage o Fracture Streak Color of the mineral in powdered form Does not vary Graphite has a silver gray streak Another example o Hematite Redish o Magnetite jet black Crystal Form External expression of the internal molecular geometry o Quartz has a hexagonal crystal form o Note if crystals are broken you may not be able to see the original crystal form Luster Appearance of a mineral in reflected light Two basic categories o Metallic looks like a metal May be shiny metallic brassy silvery etc May be dull metallic may look rusty unpolished metal o Nonmetallic Everything else Terms used to describe silky earthy pearly o Submetallic Ex metallic luster o Pyrite Fool s Gold Ex Nonmetallic Luster o Talc Pearly luster Hardness The resistance to abrasion of scratching All minerals are compared to the Mos Scale of Hardness This is a relative scale so a mineral is considered harder than or softer than For ex o If you can scratch a mineral with you nail it is softer than 2 5 Cleavage Describes the tendency of a rock to break along preferred planes of weakness These planes of weakness can be described as where the atomic bonding between atoms in the crystal structure is week and it is at those points that the mineral breaks Fracture Is a mineral property where the atomic bonding between atoms in the crystal structure is perfect with no weakness Fracture is basically either conchoidal or non conchoidal All minerals exhibit fracture but when very strong cleavage is present it can be difficult to see Cleavage and fracture are mineral properties that describe the way a mineral breaks but not the same thing Other Properties Specific Gravity o Density compared to water Reaction to hydrochloric acid Natural magnetism Smell Taste Double refraction Malleability elasticity etc Mineral Classification Silicate minerals o Are the most abundant mineral in the earth s crust making up about 92 o Same fundamental building block the silicon oxygen tetrahedron o Four oxygen ions surrounds a smaller silicon ion Non Silicate Minerals o Not as common o Provide lead iron aluminum other metals o Salt for food plaster drywall etc