Mineralogy Minerals and crystals
World’s largest crystals: A cave in the Naica Lead Zinc mine, Mexico
Miners in Cueva de los Crystals: the mineral gypsum Crystals of a variety of gypsum (CaSO 4.2H 2 O) precipitated from hot water at 60 degrees celsius in a limestone cave in the Naica mine
Minerals Tourmaline on Feldspar Emerald Beryl (Be 3 Al 2 (SiO 3 ) 6
Crystal Shapes Halite (NaCl) Diamond (C) Quartz (SiO 2 ) Garnet (Fe 3 Al 2 Si 3 O 12 ) Stibnite (Sb 2 S 3 ) Calcite (CaCO 3 )
Pyrite (FeS 2 ) crystals
Feldspars – two of the most important rock-forming minerals Plagioclase Albite – NaAlSi 3 O 8 Anorthite CaAl 2 Si 2 O 8 K-feldspar KAlSi 3 O 8 Microcline Orthoclase Sanidine
Colours and forms of quartz Milky quartz Rose quartz Amethyst Citrine
Quartz crystals displaying prism and pyramid faces
Faces display consistent angular relationships Quartz Crystal Angles measured with a goniometer Prism Pyramid
Crystals have ordered arrangements of atoms Order Disorder
X-ray beam splits into numerous smaller beams. Interference of waves of different beams produces a diffraction pattern on a screen or film. The pattern indicates the spacing and arrangement of atoms. X-ray diffraction
Surface of galena (PbS) imaged With an atomic force microscope Atomic structure of galena (PbS) Sulphur Lead
The atomic structure of halite (NaCl) Ionic bonding
Ionic bonding – transfer of electrons Cation + Anion -
Relative sizes of ions Ion co-ordination
The atomic structure of diamond Covalent bonding
The source of Diamonds Kimberlite containing diamond The ‘Big Hole’ at Kimberly, South Africa
Cutting diamonds
Covalent bonding – sharing of electrons
Atomic structure of graphite Covalent bonding within sheet Van der Waal’s bonding between sheets
Ice Crystals Hydrogen bonding
The silicon tetrahedron
Silicate Structures Inosilicate (Single chain) Sheet silicate Nesosilicate (Double chain) Framework silicate SiO SiO 3 2- Si 4 O SiO 2 Si 4 O
(Fe,Mg) 2 SiO 4 Nesosilicate Olivine
Diopside CaMgSi 2 O 6 Hypersthene (Fe,Mg)SiO 3 Inosilicate (Single Chain) Pyroxene
Inosilicate (Double Chain) Amphibole Tremolite Ca 2 Mg 5 Si 8 O 22 (OH) 2 Riebeckite Na 2 Fe 5 Si 8 O 22( OH) 2 Tigers Eye
Sheet Silicate Biotite KAl(Fe,Mg) 3 Si 3 O 10 (OH) 2 Muscovite KAl 3 Si 3 O 10 (OH) 2
Asbestos Uses and risks (Insulation, heat, fire resistance) Serpentine (Mg 3 Si 2 O 5 (OH) 4 Chrysotile (Mg 3 Si 2 O 5 (OH) 4
Framework Silicate Quartz SiO 2 Plagioclase Albite NaAlSi 3 O 8 Anorthite CaAl 2 Si 2 O 8 K-feldspar KAlSi 3 O 8 Amethyst SiO 2
Relationship of Quartz structure to Feldspar Structure Imagine four SiO 2 molecules 4 x SiO 2 = Si 4 O 8 Substitute Al 3+ for Si 4+ in one of these molecules SiO 2 +AlO 2 +SiO 2 +SiO 2 = AlSi 3 O 8 - Add Na + or K + to supply missing charge = NaAlSi 3 O 8 or KAlSi 3 O 8 SiO 2 +AlO 2 + SiO 2 = Al 2 Si 2 O 8 2- Add Ca 2+ to supply missing charge = CaAl 2 Si 2 O 8 Albite K-Feldspar Anorthite