GEOL102.24p-Topic2_Minerals (1).pdf

Topic 2: Minerals What Is a Mineral? a naturally-occurring, inorganic, crystalline solid with a definite, but sometimes variable, chemical composition the building blocks of all rocks, i.e. all rocks are composed of one or more minerals ice pyrite malachite Source: http://www.mindat.org/ Elements & Minerals elements are the fundamental building blocks of all minerals all minerals are composed of one or more http://www.chemicool.com/ pyrite elements [FeS2] malachite ice [Cu2CO3(OH)2] [H2O] Naturally-occurring & Inorganic minerals are formed in nature, by geological processes not produced by living organisms (inorganic) - example: diamond [C] natural natural synthetic © Rob Lavinsky Crystalline Solid the atoms composing minerals are arranged in an orderly, repeating, three-dimensional structure Source: Steven Earle (2015) CC BY 4.0 Source: College Physics (2012), OSCRiceUniversity, OpenStaxCollege. CC BY 4.0. Chemical Composition a mineral’s chemical composition is its chemical formula chemical composition of a mineral is either fixed or varies within defined limits some minerals have fixed compositions - examples: halite [NaCl] or quartz [SiO2] others can exhibit a range of compositions - example: feldspar [(K,Na)AlSi3O8] potassium sodium feldspar feldspar [KAlSi3O8] [NaAlSi3O8] Source: Wikipedia Commons Source: imgur.com Impurities in Minerals impurities (minor quantities of other elements - also called "trace elements") can alter the appearance of minerals - example: different varieties of corundum [Al2O3] include ruby and sapphire, which have different colours (and value!) due to impurities Sapphire Ruby [Al2O3 + Fe/Ti] Corundum [Al2O3] [Al2O3 + Cr] Source: http://www.mindat.org/ Mineral vs. Compound compounds can be organic; all minerals are inorganic compounds don’t necessarily have regular crystal structures, i.e. they don’t have to be solid (e.g. liquid water is a compound); all minerals are solid compounds and minerals can be produced naturally or synthetically in a lab; minerals always occur naturally minerals are a subset of compounds How do minerals form? minerals form by crystallization, where atoms of a gas or liquid combine to form a solid crsystallization can occur in many ways, e.g. cooling of a molten rock (magma) or precipitation from a fluid Source: Wikimedia user JJHarrison (2009) CC BY-SA 2.5 Classes of Rock-Forming Oxides Hematite [Fe2O3] Minerals Images Silicates Carbonates Sourced Calcite [CaCO3] from: Feldspar [KAlSi3O8] mindat.org Native Elements Copper [Cu] Halides Sylvite [KCl] Phosphates Image source: Apatite [Ca5(PO4)3(F,Cl,OH)] Wikimedia user Digon3 (2009) Sulfides CC BY-SA 3.0 Pyrite [FeS2] Sulfates Gypsum [CaSO4·2H2O] Source: www.britannica.com Carbonates carbonate ion (CO32-) is the building block of carbonates Example: calcite most common carbonates: - calcite: CaCO3 - dolomite: CaMg(CO3)2 Source: Karla Panchuk (2018) CC BY-SA 4.0. Photos by Rob Lavinsky, iRocks.com, CC BY-SA 3.0. Oxides oxygen is bonded to atoms or cations of other elements - examples: Fe3+, Cr3+, Ti4+ oxides are a principal source of metals for industry Spinel [MgAl2O4] Hematite [Fe2O3] Uraninite [UO2] Gem mineral Image Sources: mindat.org Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Photos by R. Weller/ Cochise College. Sulfides basic building block is the sulfide anion (S2-) - bonded to metallic cations principal ore of many valuable metals: - chalcopyrite [CuFeS2] - sphalerite [ZnS] - millerite [NiS] sulfide mineral weathering is a global environmental issue Image source: Mike Moncur (2006) https://uwaterloo.ca/ Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Photos by R. Weller/ Cochise College. Sulfates include sulfate ion (SO42-) bonded with cationic metals - examples: Ca2+, Ba2+, Mg2+, Fe2+ and others commonly occur in high-evaporation environments, e.g. deserts (evaporite deposits) common examples: Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Mineral Hydration some minerals incorporate water molecules in their crystal structure ("hydrated") Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. still classified within the various mineral classes, e.g. gypsum is a hydrated sulfate mineral Source: thefactfactor.com Halides halide anions bonded to metallic cations - anions: F-, Cl-, Br-, I- - cations: Na+, K+, Ca2+, Mg2+ halide minerals commonly occur in evaporite deposits economic examples: - halite: NaCl - fluorite: CaF2 - sylvite: KCl (potash) Image Source: PotashCorp. http://upload.wikimedia.org/wikipedia/commons/0/0c/Mineral_Silvina_GDFL105.jpg Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Native Elements often occur in very small amounts in rock (e.g. gold) example of native gold - “gold nuggets” not all metals are present in nature as native elements Native Silver http://www.mineralogicalrecord.co m/newpix/Silver,-Morocco.jpg Gold nugget – goldrushnuggests.com Gold in quartz – Wikipedia Commons Native Platinum https://www.crystalclassics.co.uk/produ ct/native-platinum-6570/ Source: Karla Panchuk (2018) CC BY-SA 4.0. Silicates silicate minerals comprise ~90% of Earth’s crust - also account for ~1/3 of all known minerals basic building block of all silicate minerals: silicon-oxygen tetrahedron (SiO4-4) - silicon ion (Si4+) surrounded by four oxygen ions (O2-) -4 SiO4 Image from Fletcher, Gibson & Ansdell (2014) Introduction to Physical Geology, Canadian Edition. Wiley. Silicates silicate minerals are subdivided into several major groups depending on how their silicon-oxygen tetrahedra are arranged in the crystal structure, e.g. - framework silicates - chain silicates - sheet silicates Image from Fletcher, Gibson & Ansdell (2014) Introduction to Physical Geology, Canadian Edition. Wiley. Framework Silicates Si-O tetrahedra form a three- dimensional framework - minerals tend to be very hard (and strong) this group comprises ~75% of the earth's crust important examples: - quartz [SiO2] - feldspar: - K-feldspar [K(AlSi3)O8] - plagioclase [Na(AlSi3)O8] Image from Fletcher, Gibson & Ansdell (2014) [Ca(Al2Si2)O8] Introduction to Physical Geology, Canadian Edition. Wiley. !%" " % !$!#& "!#! Chain Silicates Images from Fletcher, Gibson & Ansdell (2014) Introduction to Physical Geology, Canadian Edition. Wiley. single-chain double-chain Si-O tetrahedra form single or double chains chemical composition can vary based on cation substitutions, e.g. K+, Na+, Ca+2, Mg+2, Fe+2, Fe+3 silicate chains tend to strengthen crystal structure in 1 direction, but planes of structural weakness can develop in other directions Pyroxene (augite) (Ca,Na)(Mg,Fe,Al,Ti)(Si,Al)2O6 Amphibole (hornblende) (Ca,Na)2(Mg,Fe,Al)5(Al,Si)8O22 (OH)2 Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Photos: sandatlas.org / e-rocks.com Sheet Silicates continuous sheets of Si-O tetrahedra form a layered hexagonal network - spaces between the layers can be occupied by a variety of cations, e.g. K+, Na+, Ca+2, Mg+2, Fe+2, Fe+3 silicate layers are strong within Image from Fletcher, Gibson & Ansdell (2014) Introduction to layer but very weak between Physical Geology, Canadian Edition. Wiley. layers, e.g. layers can easily "slide" on each other examples: mica - biotite (brown, black) - muscovite (grey, white) Wikipedia Creative Commons CC BY 4.0 Source: Karla Panchuk (2018) CC BY-NC-SA 4.0. Top left- modified after Steven Earle (2015) CC BY 4.0. Top right- modified after Klein & Hurlbut (1993). Photos by R. Weller/ Cochise College Physical Properties of Minerals used to identify minerals in field and laboratory colour hardness cleavage / fracture lustre streak specific gravity (density) crystal form other properties (e.g. magnetism, acid reaction) Sources: mindat.org and Wikipedia Commons Colour some minerals have a distinct colour pyrite turquoise however, many others display a range of colours, e.g. - quartz [SiO2] quartz (amethyst) quartz (citrine) - K-feldspar [KAlSi3O8] K-feldspar K-feldspar *** BUT colour is not always reliable for mineral identification!! Source: Wikipedia Commons Silicate Colours light – "felsic" (important: remember this!!) - high Si content; low Fe + Mg content - examples: feldspar, quartz feldspar & quartz dark – "mafic" (important: remember this!!) - high Fe + Mg content; lower Si content - examples: amphibole, pyroxene amphibole & pyroxene ocean crust (mafic) continental crust - rich in mafic (felsic) - enriched minerals in felsic minerals Hardness evaluated using Mohs scale of mineral hardness (1-10) - based upon how easily a mineral surface can be scratched Image from Fletcher, Gibson & Ansdell (2014) Introduction to Physical Geology, Canadian Edition. Wiley. "The Geologist Can Find Amazing Fossils Quickly Through Correct Diggings" Cleavage the way a mineral tends to break along planar surfaces determined by its crystal structure surfaces known as "cleavage planes" caused by the planar alignment of weaker bonds between atoms in the crystal lattice how to distinguish cleavage planes from fractures? Cleavage Fracture surfaces generally smooth surfaces generally curved, and planar broken, and rough surfaces are often reflective surfaces are non-reflective Cleavage vs. Crystal Faces cracks in this mineral are cleavage planes, repeating throughout in the same pattern cleavage plane crystal face (not cleavage) - repeated - single surface Cleavage (mica) Source: Karla Panchuk (2018) CC BY-SA 4.0. Cleavage diagram modified after M.C. Rygel (2010) CC BY-SA 3.0 Cleavage Planes mica (sheet silicate) halite (halide) pyroxene (single-chain silicate) amphibole calcite (carbonate) (double-chain silicate) (salt) Source: Karla Panchuk (2018) CC BY-SA 4.0. Cleavage diagrams modified after M.C. Rygel (2010) CC BY-SA 3.0 Fracture found in minerals with no naturally occurring planes of weakness (e.g. some framework silicates) mineral tends to break along curved or irregular surfaces example: quartz Lustre a description of how light interacts with a mineral surface a variety of descriptors can be used, e.g. - metallic - shiny like metal - vitreous - clear (or nearly clear) like glass - adamantine - like the brilliant sparkle of diamonds lustre can vary across different samples of the same mineral (be careful in mineral ID) Image Sources: https://en.wikipedia.org/wiki/Lustre_(mineralogy) Lustre Terms GREASY METALLIC RESINOUS pyrite amber (note: not a opal jade mineral, but good example of resinous!) VITREOUS SILKY ADAMANTINE PEARLY gypsum mica diamond halite quartz https://en.wikipedia.org/wiki/Lustre_(mineralogy) Streak colour of the powdered mineral by scratching the mineral on an abrasive surface, you can obtain a "streak" of mineral powder abrasive surface is typically a white ceramic plate ("streak plate") hematite colour of the powdered streak can help to identify minerals often useful for minerals with Fool’s gold! metallic lustre mineral must be softer than streak plate! pyrite Specific Gravity ratio of density of a mineral (in g/cm3) relative to density of water (1 g/cm3) specific gravity is unitless some minerals will definitely seem heavier than others! strongly related to the chemical composition of the mineral Galena [PbS] Specific Gravity Mineral Formula (unitless) galena PbS 7 calcite CaCO3 2.7 feldspar NaAlSi3O8 2.61 quartz SiO2 2.65 Rob Lavinsky, iRocks.com – CC-BY-SA-3.0 gold Au 19.2 Crystal Form geometry of a crystal - external expression of internal arrangement of atoms in crystal structure - shape of crystal or crystal cluster Other Useful Mineral Properties for ID magnetism - magnetite [Fe3O4] reaction to acid - carbonates smell - sulfur taste BUT DON’T LICK THE ROCKS - salty: halite [NaCl] Many minerals contain toxic metals! Not to mention the ones in labs have been - bitter: sylvite [KCl] handled by hundreds of students… Summary – Minerals definition of a mineral - a naturally-occurring, inorganic, crystalline solid all minerals composed of one or more elements - small impurities can change mineral properties! several classes of minerals, e.g. silicates, carbonates, oxides, sulfides, sulfates, halides, native elements silicates comprise 90% of the earth's crust - basic building block: Si-O tetrahedron silicate mineral groups based on arrangement of Si-O tetrahedra (framework silicates, single & double-chain silicates, sheet silicates) Summary – Minerals physical properties of minerals useful in identifying minerals in the field or lab - colour - - cleavage / fracture - lustre - streak - specific gravity - crystal form - other properties (e.g. magnetism, acid reaction) Note: This course will not cover all of the material in Suggested Readings each chapter of the textbook. These reading recommendations highlight Textbook material relevant to this course. Chapter 5 Introduction Section 5.1: Electrons, Protons, Neutrons, and Atoms Section 5.3: Mineral Groups Section 5.4: Silicate Minerals Section 5.5: Formation of Minerals Section 5.6: Mineral Properties Workbook Chapter 5 - vocabulary and review questions Additional Materials: Minerals The Evolution of Minerals and Life - an interesting article featuring an interview with a distinguished mineralogist who discusses his thoughts on how minerals may have formed in the early history of universe and whether minerals can evolve with time, just like life

GEOL102.24p-Topic2_Minerals (1).pdf

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