Igneous Minerals l l l We will be

Igneous Minerals l l l 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 l Differntiate magma based on it’s chemical composition felsic vs. mafic

Melt Composition + ‘freezing’ T l l Liquid magma freezes into crystals the composition of what freezes first is governed by the melt’s composition Analogous to the composition of seawater 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

l l Ca 2+ O 2 Si 4+ O 2 - Mg 2+ Na+ Fe 2+ Liquid hot O 2 MAGMA 2 O O 2 - Si 4+ O 2 - Si 4+ 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 Mg 2+ O 2 - cooling rock Mg 2+ Fe 2+

Mineral Structures Silicates are classified on the basis of Si-O polymerism [Si. O 4]4 - Isolated tetrahedra Nesosilicates Examples: olivine garnet [Si 2 O 7]6 - Paired tetrahedra Sorosilicates Examples: lawsonite n[Si. O 3]2 - n = 3, 4, 6 Ring silicates Cyclosilicates Examples: benitoite Ba. Ti[Si 3 O 9] axinite Ca 3 Al 2 BO 3[Si 4 O 12]OH beryl Be 3 Al 2[Si 6 O 18]

Mineral Structures Chain Silicates – single and double [Si. O 3]2 - single chains pryoxenes pyroxenoids Inosilicates [Si 4 O 11]4 Double tetrahedra amphiboles

Mineral Structures Sheet Silicates – aka Phyllosilicates [Si 2 O 5]2 Sheets of tetrahedra micas talc clay minerals serpentine Phyllosilicates

Mineral Structures Framework silicates – aka Tectosilicates low-quartz [Si. O 2] quartz 3 -D frameworks of tetrahedra: fully polymerized feldspars feldspathoids zeolites Tectosilicates

Characterizing minerals l 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 F Feldspar group, mica group, feldspathoid group F l Sites – designated M 1, M 2, etc. – designate spots where cations go into structure F different site designations have different characteristics (‘see’ different charge, have different sizes, etc. ) and accommodate different ions based on this

Equilibrium l l 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 l l Thought experiment: Put pure H 2 O 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