CHAPTER 1: MINERALS: DEFINITION, PROPERTIES AND OCCURRENCES Sarah Lambart
CONTENT OF CHAPTER 1 Goal: learn how to describe and classify minerals 3 elements of classification: chemistry, structure and environment Outline: Occurrences of minerals Classification of minerals Physical properties of minerals
Definitions: A mineral is always (1) inorganic, (2) naturally occurring, (3) with a structure and a composition that give it defined macroscopic properties. A mineral is most of the time a (1) crystal and (2) a solid. A crystal is a homogeneous chemical compound with a regular and periodic arrangement of atoms. These arrangements present symmetries. A crystal is not always a mineral. It can be synthetic or organic (e.g., proteins)
MINERAL OCCURRENCES AND ENVIRONMENTS Igneous Half dome, Yosemite (granite) Sedimentary Montaña de Oro State Beach (shales) Metamorphic Sequoia National Forest California (marble, schist and gneiss)
COMMON MINERALS & MINERAL ASSOCIATIONS Metamorphic Omphacite (amphibole) Jadeite (pyroxene) Epidote, chlorite Sedimentary Carbonates (calcite, dolomite, ) Salts (halite) Gypsum Igneous: Olivine + pyroxenes Plagioclases + pyroxenes
ADDITIONAL SLIDE Minerals in igneous rock Acid (SiO 2 >63 wt. %) Rock names Rhyolite, granite (intrusive, extrusive) Common minerals Quartz, alkali feldspar (plagioclase, hornblende, micas) Intermediate (52<SiO 2 <63 wt. %) Andesite, dacite, diorite, tonalite, Sodic plagioclase (hornblende, biotite, quartz, pyroxene). Basic (45<SiO 2 <52 wt. %) Basalt, gabbro, pyroxenites pyroxene, plagioclase, (Olivine, iron oxide, titanium oxide, quartz, amphibole, micas) Ultrabasic (SiO 2 <45 wt. %) Peridotite, kimberlite Olivine, pyroxene (plagioclase garnet, amphibole, spinel, micas)
ADDITIONAL SLIDE Minerals in sedimentary rocks Clastic sedimentary rocks Conglomerates and breccias (>2mm) Sandstones (0.06-2mm) Mudrocks (<0.06mm) quartz, gold, diamond, apatite, calcite, and clays Chemical sedimentary rocks Siliceous rocks (silex) Evaporite Limestone, dolostone Organic sedimentary rocks Carbonate rocks (guano, coal) calcite, gypsum, anhydrite, halite and sylvite, borate minerals phosphates, graphite, calcite, fossils
ADDITIONAL SLIDE Minerals in metamorphic rocks Basic rock (basalt, gabbro) Clay-rich sedimentary rock (shale, mudstone) Limestone Metabasite Metapelite Marble Amphiboles +epidote for LMG +plagioclase for HMG Muscovite + Quartz +chlorite, biotite garnet for LMG +sillimanite, opx, cordierite for HMG Calcite or dolomite +micas, quartz, clay, pyrite
CLASSIFICATION AND NAMING >4000 mineral species Classification: based on the dominant anion
Sulfates: with SO 4 2- Phosphates: with PO 4 3-, (or AsO 4 3-,VO 4 3- ) Borates: with BO 3 2- (or BO 4 5- ) Gypsum (CaSO 4 2H 2 O). Apatite Ca 5 (PO 4 ) 3 (OH) Borax Na 2 B III 2 BIV 2 O 5 (OH) 4 8H 2 O Oxide: Cation + oxygen Hydroxides: with OH - Carbonates & nitrates : with CO 3 2- (or NO 3- ) hematite (Fe 2 O 3 ) Ex.: magnetite (Fe 3 O 4 ) Brucite Mg(OH) 2 Ex.: gibbsite Al(OH) 3 Calcite CaCO 3 Ex.: Nitratite NaNO 3
Native: no anion Sulfide: with S 2-, (or As, Te) Halides: contained halogens (F, Cl, Br, I) Gold (Au) Ex.: Pt, Ag, Cu, C(graphite or diamond) pyrite(fes 2 ) Ex.: galena (PbS 2 ), sphalerite (ZnS) table-salt (NaCl) Ex.: Fluorite (CaF 2 ) Silicates: with SiO 4 4-
SILICATES Orthosilicates Olivine (Fe,Mg)2SiO4 Ex.: pyrope Mg3Al2Si3O12 Chain silicates Amphibole Sorosilicates Epidote Ca2Al2FeO(OH)SiO4 Si2O7 Sheet silicates Muscovite Cyclosilicates Tourmaline Framework silicates (or tectosilicates) Quartz SiO2 Ex.: Feldspar NaAlSi3O8
DIAGNOSTIC PROPERTIES - Habit - Morphology - Transparency - Luster - Color - Streak - Tenacity - Cleavage and fractures - Density - Hardness - Others
PHYSICAL PROPERTIES Habit Euhedral Subhedral Anhedral Tabular/platy Prismatic, acidular, fibrous Morphologies: Granular
Transparency Transparent (quartz) Luster Translucent (garnet) opaque (lapis-lazuli) Metallic (pyrite) Submetallic (rutile) Adamantine (diamond) Resinous (amber) Vitreous (amethyst quartz) Earthy (desert flower)
ADDITIONAL SLIDE Luster examples
Color Streak Smithsonian collection (D.C.) Tenacity Credits: http:// depthome.brooklyn.cuny.edu/ geology/core332/minerals.htm Definition: the ability of a mineral to deform plastically under stress: Brittle > Sectile > Ductile
Cleavage Definition: Cleavage = plane of weakness. Fracture Conchoidal fractures (obsidian) Density (or specific gravity) Most silicates have a density between 2.6 and 3.5 g/cm 3
Hardness Mohs scale Moh s scale 1 Talc 2 Gypsum 3 Calcite 4 Fluorite 5 Apatite 6 Orthoclase 7 Quartz 8 Topaz 9 Corundum 10 Diamond Fingernail: 2.5 Copper penny: 3 Window glass: 5.5 Steel nail: 6.5
Other properties Taste Magnetism: magnetite (Fe 3 O 4 )> ilmenite (FeTiO 3 ) > pyrolusite (MnO 2 ) Acid-test: Calcite Fluorescence (Fluorite (CaF 2 ), calcite (CaCO 3 ), nepheline) Radioactivity (uraninite (UO 2 ), thorite (ThSiO 4 ), carnotite) Pleochroism Electrical conductivity