1. Introduction to Mineralogy Dr. Tark Hamilton Chapter 2: Lecture 5 Camosun College GEOS 250 Lectures: 9:30-10:20 M T Th F300 Lab: 9:30-12:20 W F300

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

3. 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

4. Crystals affect light Slows velocity Has density Absorbs Diffracts Refracts Excites and emits

5. Crystallography External & internal crystal form Methods: Visual, microscopy, refraction, XRD, ED, SEM, TEM Forms: Pedion, Pinacoid, Dome; (hkl) Dihedral angles: (<180°, internal) Symmetry elements: 2- 3- 4- 6-rotation, screw axes, mirror planes, glide planes

6. Light interactions with Minerals p.289 Steep angle High R.I. Short wave Flaws & inclusions Excited electrons Return lower energy Longer waves I can’t believe I missed all the electrons! Internal reflections Look out mineral here I come! Refraction bent, shorter & slower Dispersion Kinky colour effects

7. 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

8. 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

9. Lustre: appearance in scattered + reflected light (interaction between photons of visible light and bonding electrons in mineral) Metallic: Highly lustrous & reflective, polished silver, native metals, metallic minerals especially S -2, Se -2, Te -2, As -2 or -3 ; (Ag, Au, Cu, Graphite, Arsenopyrite Bornite Galena Molybdenite Pyrite) Reason: Abundant d- or f-block metallic conduction band electrons of nearly equal energy in heavy or metallic elements. Also conductive of electricity & heat.

10. Lustre: appearance in scattered + reflected light (interaction between photons of visible light and bonding electrons in mineral) Sub-metallic: Somewhat or darkly lustrous & reflective, some sulphides & oxides often with internal reflections & reddish glints; cassiterite, hematite, ilmenite, sphalerite, spinel Reason: Abundant metals in structure yet large space for transparent O -2 or S -2

11. Lustre: appearance in scattered + reflected light (interaction between photons of visible light and bonding electrons in mineral) Non-metallic: various, glassy ceramic-like, transparent or translucent silicates & p-block oxy-acid salts (sulphate, carbonate, phosphate etc.) Quartz, feldspar, zeolite, clays, calcite, dolomite, gypsum, apatite Reason: Abundant oxide & light elements often ionically or covalently bonded, non-conductive.

12. Non-metallic Lustre: various Adamantine: Brilliant, gem-like, due to high refractive index & internal reflections; diamond, garnet, cerussite, synthetic gems YAG, spinels Vitreous: Glassy transparent or translucent with high polish in silicate minerals of light elements; quartz crystal, emerald, beryl, topaz, K-feldspars Pearly: Iridescent sheen like Mother of Pearl, Abalone, internal reflection planes off of cleavages, twins, or compositional changes; apophyllite, talc

13. Non-metallic Lustre: various Resinous: translucent with internal reflections like amber, plastics or epoxies; sphalerite Greasy: Oil like surface sheen due to pitting or microscopic surface roughness in weathered silicates & salts; milky quartz, nepheline, halite, sylvite Silky: Internal reflections from individual mineral fibers in fibrous aggregates resembling silk threads or satin weaves; satin spar gypsum, serpentine, crocidolite tiger’s eye Earthy: Dull translucent aggregates of fine particles with variable air & water content like soils; limonite, kaolinite, goethite

14. 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!

15. Colour has many causes Depends on Chemical composition either essential or accidental elements (Fe is dark, Ti tints Amethyst) Depends on structure (e - in void in fluorite, graphite vs diamond) For essential elements, colour is diagnostic as for reflectance in metallics (S in sulphur, Cu ions blue in azurite, Au 2 is gold, molybdenite is silvery blue, galena is lead blue-grey)

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

17. Minerals with characteristic Colour Varietal gems: Beryl: aquamarine Blue, emerald Green Corundum: sapphire Blue, ruby Red Jadeite: light Green Quartz: adventurine Green, citrine Yellow Topaz: Yellow

18. Colours vary in non-metallics Colour zonation: fluorite, tourmaline K-Feldspar: white, yellow, tan, green, pink Plagioclase: white, grey, blue-green, black Garnet: red, brown, black, green Pyroxene: white, lt-green, dk-green, black Quartz: white, yellow, green, purple, black Calcite: white, tan, grey, blue, black

19. Play of Light & Colours Asterism, Chatoyancy: bright bands across fibers or inclusions, star sapphire, cats eye (alexandrite), tigers eye Iridescence: diffraction sheen like oil film Tarnish: thin oxide coating on metallics Labradorescence: twin planes in Ca Plag Opalescence: diffraction from grid of amorphous spheres of SiO 2 & H 2 O

20. Diffraction of white light by Precious Opal Play of colours depends on d and Θ theta

21. 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

22. Hi E  Low E Fluorescence or X-rays, Cosmic rays What happens to the rest of the energy?