Recognition and Description of Minerals - Knowns ISOTROPIC MINERALS Halite NaCl Sylvite KCl Fluorite CaF2 Periclase MgO 2+ 3+ Garnet (Ca,Mg,Fe ,Mn)3Al,Fe ,Cr)2(SiO4)3 ERSC 2P22 – Brock University Greg Finn Recognition and Description of Minerals - Knowns UNIAXIAL MINERALS Quartz SiO2 Calcite CaCO3 Nepheline NaAlSiO4 Apatite Ca5(PO4)3(F,Cl,OH) Zircon ZrSiO4 Tourmaline Boro-Silicate ERSC 2P22 – Brock University Greg Finn Recognition and Description of Minerals - Knowns BIAXIAL MINERALS Olivine (Mg,Fe)2SiO4 Orthopyroxene (Mg,Fe)2Si2O6 Clinopyroxene (Ca,Mg,Fe,Al)2Si2O6 Hornblende Ca2(Mg,Fe,Al)5Si8O22(OH)2 Tremolite Ca2Mg5Si8O22(OH)2 Actinolite Ca2Fe5Si8O22(OH)2 Biotite K2(Mg,Fe)3AlSi3O10(OH,F)2 Muscovite KAl2(AlSi3O10)(OH)2 Chlorite (Mg,Al,Fe)3(Si,Al)4O10(OH)2*(Mg,Al,Fe)3(OH)6 Plagioclase (Na,Ca)Al(Al,Si)Si2O8 Alkali Feldspar KAlSi3O8 ERSC 2P22 – Brock University Greg Finn 1 Features Useful in the Identification of a Mineral • Shape of grains • Degree of crystallinity • Cleavage • Twinning • Alteration • Associations ERSC 2P22 – Brock University Greg Finn Shape of grains • Acicular needle-like grains (actinolite, tremolite) • Bladed elongate, slender (hornblende) • Columnar elongate with equidimensional cross sections (quartz, pyroxenes) • Equant equidimensional grains (quartz, olivine) • Fibrous grains form long slender fibers (asbestos, sillimanite) • Lathlike flat elongate grains (plagioclase) • Prismatic crystal faces defined by prism (apatite) • Tabular book shape (plagioclase) ERSC 2P22 – Brock University Greg Finn Bladed Grains Hornblende © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn 2 Equant Grains qtz qtz © G.C. Finn, 2005 © G.C. Finn, 2005 ol ol © G.C. Finn, 2005 © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn Fibrous Grains bio bio sill sill © G.C. Finn, 2005 © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn Lath-like Grains pl pl cpx cpx pl pl pl pl cpx cpx © G.C. Finn, 2005 © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn 3 Prismatic Grains ap © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn Degree of Crystallinity • _________ • grains have well formed crystal faces • _________ • poorly formed and/or irregular crystal faces • _________ • no regular crystal faces ERSC 2P22 – Brock University Greg Finn Cleavage • In grain mounts, ______________ on grains indicate the presence of _________ • In thin section, cleavage is difficult to recognize in minerals with a low relief, under normal circumstances • By closing the aperture diaphragm cleavage is more readily seen ERSC 2P22 – Brock University Greg Finn 4 Cleavage • Grains at the edge of the section may exhibit cleavage more so than grains in the centre • _______ between cleavages is useful for identifying the broad mineral group – Pyroxene - 2 at 90° – Amphibole – 2 at 56°/124° – Alkali Feldspar - 2 at 90° – Plagioclase – 2 cleavages at 94° ERSC 2P22 – Brock University Greg Finn Cleavage pl © G.C. Finn, 2005 bio hbl © G.C. Finn, 2005 © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn Twinning •Presence and nature of the twins may be ___________ •A variety of twin laws may be observed in thin section ERSC 2P22 – Brock University Greg Finn 5 Simple Twin Two segments of one grain go extinct at different times on rotating the stage 0.5 mm © G.C. Finn, 2005 cpx 0.5 mm © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn Contact Joined by a smooth twin plane separating the segments Twins Carlsbad-albite Twin Plane pl © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn Penetration Twin Joined by an irregular contact 0.5 mm © G.C. Finn, 2005 staur 0.5 mm © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn 6 Polysynthetic Consists of numerous twin segments joined on parallel twin planes Twin Albite Twin pl Plane © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn Alteration •The type of alteration product observed within an individual grain may be used to identify that grain •e.g. – iddingsite alteration of olivine – sericite alteration of plagioclase – clay minerals from alkali feldspars ERSC 2P22 – Brock University Greg Finn Olivine altering to Serpentine ol ol ser ser ol ol ol ol © G.C. Finn, 2005 © G.C. Finn, 2005 ERSC 2P22 – Brock University Greg Finn 7 Plag altering to Sericite pl pl sericite sericite pl pl From: http://www.union.edu/PUBLIC/GEODEPT/COURSES/petrology/ig_minerals.htm ERSC 2P22 – Brock University Greg Finn Associations • Knowing the common mineral associations in a variety of rock types may aid in making an "educated guess" as to the identity of an unknown mineral • Knowing the mineral association for a given rock may aid in the identification of a specific mineral which might otherwise have been overlooked • Appendix C of Nesse lists the common igneous, metamorphic and sedimentary rocks and expected mineralogy in each ERSC 2P22 – Brock University Greg Finn Mineralogy of Common Igneous Rocks Rock Type Major (>10%) Minor (<10%) Accessory Allanite, apatite, epidote, Felsic Quartz, Muscovite, biotite, magnetite, ilmenite, hematite, (granite, rhyolite, hornblende fluorite, garnet, monazite, granodiorite, etc.) K-feldspar, sillimanite, tourmaline, zircon plagioclase (Ab-ol) Allanite, apatite, epidote, Intermediate Plagioclase (And), Quartz, biotite, magnetite, ilmenite, hematite, (diorite, tonalite, dacite, hornblende muscovite, opx, zircon andesite) cpx Apatite, chromite, magnetite, Mafic Plagioclase (Lab - Biotite, ilmenite, hematite, spinel (basalt, gabbro, norite, By), cpx, opx, hornblende peridotite) olivine Apatite, epidote, magnetite, Si-deficient K-feldspar, Biotite, muscovite, ilmenite, hematite, melilite, Rare- (syenite, phonolite) plagioclase (Ab- Na-amphibole, Earth minerals And), nepheline, Na-pyroxene leucite, sodalite From: Nesse 2004, Appendix C.1 ERSC 2P22 – Brock University Greg Finn 8 Mineralogy of Common Sedimentary Rocks Clastic Carbonate Evaporite Quartz Calcite Anhydrite K-feldspar Dolomite Calcite Plagioclase Clay Chalcedony Clay Glauconite Dolomite Chalcedony Clastic material Gypsum Calcite Skeletal remains Halite Muscovite Sulfur Biotite Sylvite Glauconite Clastic material Magnetite Ilmenite Hematitie Zeolites PLUS MANY MORE From: Nesse 2004, Appendix C.2 ERSC 2P22 – Brock University Greg Finn Mineralogy of Common Metamorphic Rocks Rock Type Common Accessory Quartz, plagioclase, muscovite, Apatite, epidote, graphite, hematite, ilmenite, magnetite, tourmailine Pelite (shale) chlorite, biotite, garnet, chloritoid, andalusite, kyanite, sillimanite, staurolite, K-feldspar Plagioclase, amphibole, cpx, Apatite, hematite, ilmenite, magnetite, spinel, Mafic (basalt) zircon biotite, quartz, titanite, calcite, chlorite, epidote, garnet, Calcite, dolomite, epidote, Corundum, graphite, hematite, ilmenite, magnetite, titanite Carbonate (limestone) garnet, cpx, amphibole, biotite, olivine, quartz, aragonite, wollastonite, talc, scapolite, periclase, brucite Quartz, K-feldspar, plagioclase, Allanite, apatite, epidote, garnet, hematite, ilmenite, magnetits zircon Granitic Gneiss (felsic, biotite, cordierite, hornblende, sediments) opx Quartz, plagioclase, epidote, Apatite, hematite, ilmenite, magnetite, Metagraywacke (high and prehnite, ziorcon low pressure rocks) pumpellyite, lawsonite, chlorite, biotite, stilpnomelane, muscovite, omphacite, Na- amphibole, calcite, aragonite, garnet, serpentine, titanite, zircon From: Nesse 2004, Appendix C.3 ERSC 2P22 – Brock University Greg Finn 9.