Chap 7/8: Phase Diagrams

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rock-forming minerals

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Description and Tags

25 Terms

1

rock-forming minerals

mineral group composed of the most common minerals found in earth

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2

major element

chemical elements that occur in large amounts

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3

minor elements

elements with abundances btwn 1.0 and 0.1 percent

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4

trace elements

elements that occur in smaller amounts <0.1 weight %

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5

triangular diagram

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

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6

Al2SiO5 polymorphs and their conditions

  • Kyanite, lower temperature and high pressure

  • sillimanite, high temperature

  • andalusite, low to mid temperature and low pressure

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7

polymorph definition

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

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8

two uses of the phase diagram

  • predict which phase we will find

  • use the phases to understand the temperature and pressure history

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9

tectosilicates

SiO2 polymorphs, feldspars, sodalite

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10

chain silicates (inosilicates)

tetrahedral chains

  • single - pyroxenes

  • double - amphiboles

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11

sheet silicates (phyllo)

infinitely extending tetrahedral sheets

  • talc, micas, chlorite,

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12

nesosilicates

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

  • (SiO4)4+, andalusite polymorphs

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13

sorosilicates

double tetrahedral units

  • epidote

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14

cyclosilicates

ring structures

  • beryl, tourmaline, and cordierite

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15

invariant point

can only exist at one temperature and pressure

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16

univariant line

one variable can change but all others would be fixed

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17

divariant field

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

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18

liquidus meaning

Temperature at which a mixture of minerals is completely liquid

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19

solidus

Temperature below which a mixture of materials is completely solid

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20

tie line

line in phase diagram joining coexisting minerals

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21

fractional crystallization

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

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22

solid solution

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

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23

miscibility gap

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

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24

zoning

composition changes from the inside out

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25

eutectic

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

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