2Minerals: Building blocks of rocks To be considered a mineral, a substance must:be a naturally occurring solidbe formed by inorganic processeshave a crystalline structure (orderly molecular arrangement)have a specific chemical composition
3An element is a substance that cannot be broken down into simpler substances by chemical means Minerals are made up of one or more elements
4Most abundant elements of the continental crust Common rock-forming minerals are mostly chemical compounds made up of these elementsHow do these elements combine to make minerals?
5Atoms, molecules and ions Atoms are the smallest individual particle that retains the distinctive chemical properties of an element.Molecules are the smallest individual particle that retains the distinctive chemical properties of a chemical compound. Molecules consists of 2 or more atoms.Ions are atoms or molecules that have a net electrical charge. They attract oppositely-charged ions to form chemical compounds.
6Crystalline Nature of Minerals Crystal: any substance whose atoms are arranged in a regularly repeating patternCrystal growth is often interrupted due to:lack of spacerapid cooling rate
7Luster: Appearance of a mineral in reflected light Metallic (pyrite)Nonmetallic: glassy/pearly (potassium feldspar)
8Luster: Appearance of a mineral in reflected light Nonmetallic- waxy (ex: chert)Nonmetallic –greasy (quartz)
9ColorOften highly variable for a given mineral due to slight impurities in crystal structureFor example, quartz (SiO2) exhibits a variety of colors
10Other Physical properties of minerals StreakColor of a mineral in its powdered formHelpful in distinguishing different forms of the same mineralHardnessResistance of a mineral to abrasion or scratchingAll minerals are compared to a standard scale, the Mohs Scale of Hardness.
11Streak – the color of a powdered mineral Figure 2.10
12Hardness Resistance of a mineral to abrasion or scratching All minerals are compared to a standard scale called the Mohs scale of hardness
13Cleavage Tendency to break along planes of weak bonding Produces flat, shiny surfacesDescribed by resulting geometric shapes, andNumber of planesAngles between adjacent planesCleavage is one of the physical diagnostic properties of minerals. To cleave means to break and cleavage is the tendency of a mineral to break along planes of weak chemical bonding, which we call cleavage planes.If a mineral breaks along a cleavage plane, it produces flat, shiny surfaces. If it breaks along a non-cleavage plane, the result will be jagged and irregular.
15Common cleavage directions Cleavage is described by the number of cleavage planes the angle between adjacent planes and the shape of the mineral if it breaks along cleavage planes
16Classification of Minerals Rock-forming mineralsCommon minerals that make up most of the rocks of Earth’s crustOnly a few dozen membersComposed mainly of the 8 elements that make up over 98% of the continental crust
18Classification of Minerals In most cases, minerals are grouped according to the major “building block” in the chemical structure.Silicates (SiO44-)Oxides (O22-)Sulfides (S2-)Sulfates (SO42- )Carbonates (CO32-)Halides (Cl1- , F1- Br1- )Native Elements (single element)
19Rock-forming Minerals – The Silicate Group Most common mineral group due to large amounts of silicon and oxygen in Earth’s crustBasic building block is the silicate ion: Four oxygen ions surrounding a much smaller silicon ion.Polymerization: process by which silicate ions bond to form more complex ions, such as rings, chains, sheets or 3 dimensional frameworks.
20Common Silicate minerals Olivine GroupHigh temperature Fe-Mg silicateIndividual silicate linked together by iron and magnesium ionsForms small, rounded crystals with no cleavage
21Common Silicate minerals Pyroxene GroupSingle chain structures involving iron and magnesiumTwo distinctive cleavages at nearly 90 degrees
22Common Silicate Minerals Amphibole GroupDouble chain structures involving a variety of ions linking the silicate ionTwo perfect cleavages at non right angles Hornblende is the most common mineral in the amphibole group
23Common Silicate Minerals Mica GroupSheet structures that result in one direction of perfect cleavageBiotite is the common dark colored mica.
24Common Silicate Minerals Mica GroupSheet structures that result in one direction of perfect cleavageMuscovite is the common light colored mica.
25Classification of Minerals Common Silicate mineralsFeldspar GroupMost common mineral group3-dimensional framework that exhibits two directions of cleavage at 90 degrees(potassium feldspar) (e.g. Orthoclase or Microcline)Plagioclase (sodium and calcium feldspar) are the two most common members
31Nonsilicate mineral groups Fluorite (left, calcium fluoride) and halite (right, sodium chloride) are members of the Halide mineral group. The minerals in this group have, as part of the chemical structure, an ion from the halogen elements: Fl1- , Cl1- , I1- , or Br1- .Gypsum (calcium sulfate) is a member of the sulfate group. The building block for minerals in this group is the sulfate ion, SO42- .
32The Carbonate GroupCarbonates are minerals found in exoskeletons of marine organisms.Calcite (calcium carbonate – CaCO3) is the most important carbonate mineral.It has a nearly perfect rhomboid cleavageIt will dissolve if exposed to acid (as shown in the video).“Strong bones, strong teeth”
33Nonsilicate Rock-forming mineral groups Sulfates – minerals containing the sulfate ionGypsum (Calcium sulfate: CaSO4 – 2H2O. A product of rapid evaporation of ancient seas.