Chap 7/8: Phase Diagrams

mineral group composed of the most common minerals found in earth

chemical elements that occur in large amounts

elements with abundances btwn 1.0 and 0.1 percent

elements that occur in smaller amounts <0.1 weight %

a diagram that allows for graphic representation of mineral chemistry in terms of three end member groups

• Kyanite, lower temperature and high pressure

• sillimanite, high temperature

• andalusite, low to mid temperature and low pressure

a group of minerals that have the same chemical composition but different structure

• predict which phase we will find

• use the phases to understand the temperature and pressure history

SiO2 polymorphs, feldspars, sodalite

tetrahedral chains

• single - pyroxenes

• double - amphiboles

infinitely extending tetrahedral sheets

• talc, micas, chlorite,

corner oxygens link to other cation polyhedra instead of link with other silica tetrahedra

• (SiO4)4+, andalusite polymorphs

double tetrahedral units

• epidote

ring structures

• beryl, tourmaline, and cordierite

can only exist at one temperature and pressure

one variable can change but all others would be fixed

both temperature and pressure can be varied independently without changing the number of phases

Temperature at which a mixture of minerals is completely liquid

Temperature below which a mixture of materials is completely solid

line in phase diagram joining coexisting minerals

a realistic crystallization, doesnt matter where the starting composition is as it will always end up at the same place

homogenous mixture of two different kinds of atoms in solid state and have a single crystal structure

a region in a phase diagram where the mixture exists as two or more phases, forms exsolution lamella upon cooling

composition changes from the inside out

minimum-melting composition of 2 or more components, each of which melts and freeze congruently forming a mixture of the component crystals during crystallization