Chapter 3 Minerals The Building Blocks of Rocks
Chapter Outline • Introduction • Matter–What Is It? • Explore the World of Minerals • Mineral Groups Recognized by Geologists • Geo-Insight: The Precious Metals • Physical Properties of Minerals • Geo-Focus: Welcome to the Wonderful World of Micas • Rock-Forming Minerals • How Do Minerals Form? • Natural Resources and Reserves • Geo-Recap
Introduction What is a mineral? A mineral is Naturally Inorganic Crystalline solid Characteristic physical properties Specific chemical composition. Gemstones – precious or semi-precious minerals or rocks used for decorative purposes
Introduction • Are amber and pearls minerals? • Amber is considered a semiprecious “stone,” but it is not a mineral because it is organic and not crystalline. • Pearls, although they grow in mollusks, are minerals because they are crystalline and meet the other criteria for minerals.
Matter – What is It? • Atoms and Elements • All matter is composed of chemical elements, which are themselves composed of atoms. • Atoms consist of a nucleus, of protons and neutrons, and electrons that circle the nucleus. • Elements are defined on the basis of the number of protons in the nucleus of an atom (i.e., the atomic number). • Another characteristic of an atom is its atomic mass, the sum of the numbers of protons and neutrons in the nucleus.
Matter – What is It? What are the atomic number and atomic mass of an atom? The number of protons in an atom’s nucleus determines its atomic number, whereas an atom’s atomic mass number is the total number of protons and neutrons in the nucleus. For example, if an atom has 6 protons and 8 neutrons its atomic number and mass numbers are 6 and 14, respectively.
Nucleus 6 p 6 n 6 p 7 n 6 p 8 n 12C (Carbon 12) 13C (Carbon 13) 14C (Carbon 14)
Matter – What is It? Bonding and Compounds Atoms are joined to one another by forces known as bonding. Atoms of different elements which are bonded to one another form compounds.
Matter – What is It? Bonding and Compounds Ionic Bonds - Ionic bonds transfer ions, with opposite electrical charges attracting one another Halite is a compound formed by the bonding of sodium atoms to chlorine atoms.
electron transfer Sodium atom 11 p+ 11 e– Chlorine atom 17 p+ 17 e– Sodium ion 11 p+ 10 e– Chlorine ion 17 p+ 18 e– + –
Matter – What is It? Bonding and Compounds Covalent Bonds - Covalent bonds atoms share electrons.
Matter – What is It? Bonding and Compounds Metallic Bonds Metallic bonds result from extreme electron sharing. Van der Waals bonds Van der Waals bonds are an extremely weak bond without available electrons to form an attraction.
Explore the World of Minerals Naturally Occurring Inorganic Substances We define a mineral as naturally occurring This excludes all synthetic substances made by man like synthetic diamonds and rubies. The term inorganic deserves special consideration Animal and plant matter are not minerals Certain organisms, however, do use minerals, like calcite and quartz, to form their shells
Explore the World of Minerals Mineral Crystals Why is it that not all mineral specimens show well-developed crystals but all are crystalline solids? As minerals form and grow, they may merge with one another to form a mosaic of interlocking crystalline solids that show no obvious crystals. Nevertheless, individual minerals within this mosaic have their atoms arranged in a specific three-dimensional framework.
Explore the World of Minerals Chemical Composition of Minerals By definition native elements are made up of only one chemical element, such as gold (Ag) and diamond (C). Most minerals are composed of two or more chemical elements, such as quartz (SiO²).
Mineral Groups Recognized by Geologists How Many Minerals Are There? Even though there are 92 naturally occurring elements, only 8 of them are very common in Earth’s crust. Even among these 8, oxygen and silicon are by far the most common. Most common minerals are made up of oxygen, silicon, and one or more other elements.
Mineral Groups Recognized by Geologists Most of the more than 3,500 known minerals are silicates (compounds of silicon and oxygen, and other elements). Additional common mineral groups include carbonates, oxides, sulfides, sulfates, and halides.
Mineral Groups Recognized by Geologists Silicate Minerals composed of the silica tetrahedra
Mineral Groups Recognized by Geologists Silicate Minerals Ferromagnesian silicates - made up of iron, magnesium, or both combined with other elements. dark in color and dense
Mineral Groups Recognized by Geologists Silicate Minerals Nonferromagnesian silicates - lack iron and magnesium light colored
Mineral Groups Recognized by Geologists Carbonate Minerals All carbonate minerals have the carbonate radical (CO³)-² as in calcite (CaCO³) and dolomite [CaMg(CO³)²]. Carbonate minerals are found mostly in the sedimentary rocks limestone and dolostone. Carbonates are derived from the shells and hard parts of marine organisms or are precipitated from seawater as evaporites.
Mineral Groups Recognized by Geologists Other Mineral Groups Native Elements All native elements are composed of a single element. Gold, copper and diamonds commonly occur as native elements.
Mineral Groups Recognized by Geologists Other Mineral Groups Sulfides All sulfide minerals contain sulfur plus a metallic element as in galena (PbS) and pyrite (FeS²). Sulfide minerals are found in all types of rocks. They commonly form along mid-oceanic ridges
Mineral Groups Recognized by Geologists Other Mineral Groups Sulfates All sulfate minerals have the sulfate radical (SO4 -² ) as in gypsum (CaSO4 2H2O) Sulfate minerals are common in deserts, forming from evaporation of water
Mineral composition and structure produce unique physical properties. Color Hardness Cleavage Crystal form Specific gravity Physical Properties of Minerals
Physical Properties of Minerals Luster and Color Luster is the quality and intensity of light reflected from a mineral and is characterized as metallic or nonmetallic. Color, in contrast, is a visual quality of minerals that results from the way they absorb or transmit light.
Physical Properties of Minerals Crystal Form Crystal form is useful for the identification of minerals that typically show well-developed crystals. For many other minerals, however, the crystals grow in proximity to form a crystalline mass, in which case other mineral properties such as luster, hardness, and cleavage must be used for identification.
Physical Properties of Minerals Cleavage and Fracture Mineral cleavage refers to the breakage or splitting of mineral crystals along one or more smooth planes determined by atomic structure. When used with other mineral properties, cleavage can distinguish between minerals that otherwise look much the same. Fracture refers to the irregular breakage of a mineral
Cleavage plane Cleavage in one direction Micas—biotite and muscovite Potassium feldspars, plagioclase feldspars Cleavage in two directions at right angles Halite, galena Cleavage in three directions at right angles Cleavage in three directions, not at right angles Calcite, dolomite Cleavage in four directions Fluorite, diamond Cleavage in six directions Sphalerite
Physical Properties of Minerals Hardness Mohs hardness scale Ten minerals are used to compare the hardness between all the rest.
Physical Properties of Minerals Specific Gravity (Density) - The specific gravity is a way to describe how heavy a mineral is. Specific gravity is the ratio of the weight of a mineral to an equal volume of water. For example, galena has a specific gravity of 7.58 gm/cm3. It is 7.38 times as heavy as an equal volume of water.
Physical Properties of Minerals Other Useful Mineral Properties Feel - talc Taste - halite Magnetism - magnetite Double refraction - calcite React to dilute hydrochloric acid – calcite, dolomite
Rock-Forming Minerals How do rock-forming minerals differ from accessory minerals? A few minerals are common enough to be known as rock-forming minerals. Most of these are silicates. Accessory minerals can be ignored in this endeavor because they are present in minor quantities.
Rock-Forming Minerals Common rock forming minerals
How Do Minerals Form? As molten rock material known as magma (lava at the surface) cools, minerals begin to crystallize and grow This determines the composition of various igneous rocks.
Natural Resources and Reserves How does a resource differ from a reserve? A resource is any solid, liquid, or gaseous substance in rocks whose profitable extraction is potentially feasible. Many resources are concentrations of economically important minerals. A reserve is only that part of the resource base that can be extracted economically.
Natural Resources and Reserves While the United States is dependent on imports for many mineral resources, Canada is more self-reliant.
Natural Resources and Reserves What factors affect the status or a resource? Market price is the most obvious determinate of whether a commodity is classified as a resource or reserve Other factors include geographic location, labor costs, and developments in science and technology.
Learning Objectives Upon completion of this material, the student should understand the following. • All matter, including minerals, is made up of atoms that bond to form elements and compounds. • Geologists have a specific definition for the term mineral. • You can distinguish minerals from other naturally occurring and manufactured substances. • Minerals are incredibly varied, yet only a few are particularly common. • Geologists use physical properties such as color, hardness, and density to identify minerals. • Minerals originate in various ways and under varied conditions. • Some minerals, designated rock-forming minerals, are particularly common in rocks, whereas others are found in small amounts. • Some minerals and rocks are important natural resources that are essential to industrialized societies.