Igneous Minerals We will be discussing and working in lab with the major igneous minerals and common accessory minerals We will look at putting these minerals together into rocks and ways to identify and characterize those rocks Gain a sense of what the minerals and the rocks they form tell us about the earth Volcanic provinces Hot spots Basalt flows Plutons Intrusions Magma Differntiate magma based on it s chemical composition felsic vs mafic Melt Composition freezing T Liquid magma freezes into crystals the composition of what freezes first is governed by the melt s composition Analogous to the composition of seawater ice icebergs are composed of pure water pure water freezes first leaving the concentrated brine behind In magmas More silica lower T more Ca Mg higher T Silica polymerization also affected by T and how much Si there is Back to silicate structures nesosilicates sorosilicates cyclosilictaes phyllosilicates inosilicates tectosilicates Ca 2 O2Si4 O2 Mg2 Na Fe2 O Liquid hot O2MAGMA 2O O2 Si4 O2 O2O2 Si4 O2 Discontinous series Structures change harder to re equilibrate Continuous Series plag re equilibrates quicker and if not is a continuum in composition rather than a change in mineral as T decreases Mg2 2 cooling rock Mg2 Fe2 Mineral Structures Silicates are classified on the basis of Si O polymerism SiO4 4 Isolated tetrahedra Nesosilicates Examples olivine garnet Si2O7 6 Paired tetrahedra Sorosilicates Examples lawsonite n SiO3 2 n 3 4 6 Ring silicates Cyclosilicates Examples benitoite BaTi Si3O9 axinite Ca3Al2BO3 Si4O12 OH beryl Be3Al2 Si6O18 Mineral Structures Chain Silicates single and double SiO3 2pryoxenes single chains pyroxenoids Inosilicates Si4O11 4 Double tetrahedra amphiboles Mineral Structures Sheet Silicates aka Phyllosilicates Si2O5 2 Sheets of tetrahedra micas talc clay minerals serpentine Phyllosilicates Mineral Structures Framework silicates aka Tectosilicates low quartz SiO2 3 D frameworks of tetrahedra fully polymerized quartz feldspars feldspathoids zeolites Tectosilicates Characterizing minerals WITHIN classes like the silicate classes Minerals put into groups based on similar crystal structures differing typically in chemical substitution Groups usually named after principle mineral Feldspar group mica group feldspathoid group Sites designated M1 M2 etc designate spots where cations go into structure different site designations have different characteristics see different charge have different sizes etc and accommodate different ions based on this Equilibrium Need a description of a mineral s equilibrium with it s surroundings For igneous minerals this equilibrium is with the melt magma it forms from or is a representation of the Temperature and Pressure of formation Salty Ice cube experiment Thought experiment Put pure H2O ice cube into salty water let it sit for a certain time and look at the distribution of salt inside the ice cube When the ice cube reaches a point where the concentration of salt is the same through the whole ice cube it has reached equilibium
View Full Document
Unlocking...