Introduction to Mineralogy Dr. Tark Hamilton Chapter 2: Lecture 4 Camosun College GEOS 250 Lectures: 9:30-10:20 M T Th F300 Lab: 9:30-12:20 W F300

Physical Properties of Minerals (Interplay with light) Asterism Crystal form Crystal Habit Chatoyancy Cleavage Colour Density (S.G.) Fracture Fluorescence Hardness Luminescence Lustre Magnetism Parting Phosphorescence Piezo-, Pyroelectricity Play of colours Radioactivity Tenacity Streak

Crystallography (faces) Perfect & Poor Dodecahedron 12 Pyritohedron 12 Rhombohedron 6 Perfect & Poor Cube 6 Perfect & Poor Octahedron 8

Crystallography External & internal crystal form Methods: Visual, microscopy, refraction, XRD, ED, SEM, TEM Forms: Pedion, Pinacoid, Dome; (hkl) Dihedral angles: (<180°, internal) Symmetry elements: rotation, screw axes, mirror planes, glide planes

6 Crystal Systems (Ch.6: p ) 32 Crystal Classes grouped by center of symmetry or none Triclinic: all different edges and angles, a ≠ b ≠c, no 90° angles, 1= no sym, Ī = centre Monoclinic: all different edges, a ≠ b ≠c, β > 90°, α=γ=90°, symmetry: 2,m, 2/m Orthorhombic: all different edges but all 90° angles, a≠b≠c, α=β=γ=90°: 222, mm2, 2/m 2/m 2/m Tetragonal: 2 different edges, all 90° angles, a=b≠c, α=β=γ=90°: 4, 4bar, 422, 4mm, 4bar2m, 4/m, 4/m 2/m 2/m

6 Crystal Systems (Ch.6: p ) 32 Crystal Classes grouped by center of symmetry or none Tetragonal: 2 different edges, all 90° angles, a=b≠c, α=β=γ=90°: 4, 4bar, 422, 4mm, 4bar2m, 4/m, 4/m 2/m 2/m Hexagonal (hexagonal): 2 different edges, 120° & 90° angles, a 1 = a 2 = a 3 ≠ c, α= α= α = β = 90° γ = 120°: 6, 6bar, 622, 6mm, 6bar m2, 6/m, 6/m 2/m 2/m Hexagonal (trigonal): 3 equal edges, 120° & 90° angles, a 1 = a 2 = a 3 = c, α = β = 90° γ = 120°: 3, 32, 3m, 3bar, 3bar2/m

6 Crystal Systems (Ch.6: p ) 32 Crystal Classes grouped by center of symmetry or none Tetragonal: 2 different edges, all 90° angles, a=b≠c, α=β=γ=90°: 4, 4bar, 422, 4mm, 4bar2m, 4/m, 4/m 2/m 2/m Hexagonal (trigonal): 3 equal edges, 120° & 90° angles, a 1 = a 2 = a 3 = c, α = β = 90° γ = 120°: 3, 32, 3m, 3bar, 3bar2/m Isometric (cubic): 3 equal edges, 3 90° angles, a 1 = a 2 = a 3, α = β = γ = 90°: 23, 432, 4bar3m, 2/m3bar, 4/m3bar2/m

Habit – Face Development Euhedral: good, well formed faces, taking its characteristic crystal form. E.g. hexagonal quartz prisms or cubic pyrite Subhedral: Some good faces - some curved Anhedral: Mineral lacking crystal faces, curved, rounded, embayed, irregular

Crystal Habit (Growth Shape) (Environmentally controlled) Granular Micaceous Bladed Fibrous Acicular Radiating Dendritic Mammilary Colliform Vuggy Concentric Oolitic/Pisolitic

Crystal Habit (Growth Shape) Other terms: Compact: too fine grained for naked eye e.g. Kaolinite Massive: Lacking crystal faces, multiple fine grains e.g. olivine in dunite, goethite Sugary: mass of fine crystals, e.g. gypsum, anhydrite Earthy: massive, compact, dull, e.g limonite

Crystal Habit (Growth Shape) Other terms: (and interpretation) Banded: layers with colours or compositional differences, planar version of concentric, e.g. agate, fluorite (changing fluid composition, trace elements, oxidation) Blocky: euhedral but similar in all dimensions e.g. analcite, feldspar (grew in free space or unencumbered, e.g. magmatic) Botryoidal: mammilary, reniform a curved bumpy grape-like mass with involute intersections often radial or concentric in cross section e.g. chalcedony, prehnite (growth during fluid concentration, dessication, at water table) Fibrous: thin filaments often curved e.g. asbestos (Grew in free space, across a vein)

Crystal Habit (Growth Shape) Other terms: (and interpretation) Geode: hollow rock cavity or concretionary mass with concentric layering or drusy crystals, e.g. barite, calcite, amythest often with shelves or half filled geopedal structures showing way up (shallow void or solutional space often above water table) Triple point: granular often monomineralic with 120° grain boundaries, common in quartzite & marble (equal pressure in all directions) Lamellar, foliated: layered e.g. graphite, molybdenite (pseudo- hexagonal crystal form) Needles, whiskers: Longer than wide or thick = acicular e.g. apatite, millerite (preferential growth in one direction or form, quench, bacterial)

Crystal Habit (Growth Shape) Other terms: (and interpretation) Needles, whiskers: Longer than wide or thick = acicular e.g. apatite, millerite (preferential growth in one direction or form, quench, bacterial) Prismatic: elongate euhedral forms e.g. pyroxene, amphibole, quartz (Commonly monoclinic or hexagonal) Pisolitic: Large concentric concretionary or residual masses, e.g. bauxite, cave pearls (formed at or below water table by solution precipitation processes) Tabular: similar length & width but lesser thickness e.g. feldspars (Commonly monoclinic, orthorhombic, tetragonal, grew in free space, e.g. magmatic)

Cleavage directions & forms Octahedral 109.5°Cubic 90° Dodecahedral 116.6° Prismatic 3 = (2 + pinacoid)Pinacoidal, Basal 1 Rhombohedral 3 No 90° or 60°/120°

Introduction Minerals & Light Reflectance, scattering, transmittance, refraction, absorption, energy effects…

Diaphaneity: ability to transmit light Transparent: Transmitting some light; quartz, calcite, halite, ulexite, gems Translucent: Diffuse transmittance of light, cloudy bright, bathroom glass, most silicates, sulphates, carbonates, salts; moonstone, gypsum, anhydrite, aragonite Opaque: Blocks transmittance of light even on thinnest edges, metal sulphides & oxides; Magnetite, Pyrite, Galena, Copper

Lustre: appearance in scattered + reflected light (interaction between photons of visible light and bonding electrons in mineral) Metallic: highly reflective, shiny Sub-Metallic: darkly reflective Non-metallic: various, glassy ceramic-like

Colour It is a spectral thing ROYGBIV long  short Depends on energy, E = h ν = h c/λ It depends on our eyes: Gold absorbs blue so it looks yellow!

Streak True colour of powdered mineral (depends on compound not structure)

Luminescence Mineral absorbs usually higher energy and emits cold light (not incandescence) Triboluminescence: shock emits light, quartz; hammers, explosions, quakes Thermoluminescence: heat emits light, caused by cosmic ray damage, dating use Phosphorescence: stores & emits light Fluorescence: uV emits visible light on-off