MINERALOGY BASIC CONCEPTS (PHASE DIAGRAMS) Flashcards by Sean Levi Abiera

Mechanically Separable part of the system

Phase

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display the stability fields for various phases separated by lines representing conditons under which phase changes occurs

phase stability diagrams

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Represents conditions at which phase changes occurs

Lines

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In a Phase diagram the vertical axis represents

increasing Temp

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the horizontal axis represent

variation in composition

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Phase Boundary (Line) the temperature above which the system exist 100% liquid andbelow which it contains some crystals

Liquidus

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Phase Boundary (Line) that seperates the all-solid crystals stability fied from stability which contains at least some melt

Solidus

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The space between the solidus and liquidus represents

a system which consists two types of stable phases both liquid and solid

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Gibbs Phase Rule formula

P=C+2-F

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Phases (P)

eto ung mechanically separable parts (Ilang solid individual identity) can have same component pero di magkakamukha

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Components ?

Minimum number of chemical componens required to define a phase in the system usually expressed as oxides. RULE: The lowest number of components that if i-mix will form all the phases

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Degrees of Freedom or Variance (F)

The number of independent factor that can vary (T, P, Comp) without altering te phases that are in equilibrium in one another

ito ung number of factors na pwede mong iadjust ng hindi nagbabago ung stability ng system

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Divariant

2 factors (Along stability fields)

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Univariant

1 Factor (Along Phase boudnaries)

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Invariant

no factor (Along eutectic point)

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Conditions under which LIQ. Is equilibrium with 2 DIFFERENT SOLIDS

Eutectic

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the composition of the first melt

Eutectic Pt

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Conditiona under which a RECTION occurs bweteen a PRE-EXISTING SOLID PHASE and a LIQUID MELT to produce a NEW SOLID PHASE

Peritectic

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2 melts of same composition produced by 2 rocks of different intial composition (isang anak 2 magulang)

Invariant Melting

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When a solid mineral phase is melted which produce a melt and a different mineral phase with different composition from the initial mienral

Incongruent Melting

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Mineral crystals and melt react to produce completely different mienral and there exists a NEGLIGIBLE solid soln between minerals

Discontinuous Reaction

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Mineral crystals and melt react continuously and incrementally chang the composition of both which requires a mineral solid soln series

Continuous reactions

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Phase Boundary or line that separates conditions in which complete solid sold occurs within a mineral series from conditions under which solid soln is limited. (A boundary na naghahati sa portions of na may complete solid soluton at sa portion na limited lang)

Solvus

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Silica is what type of Diagram

One Component Phase Diagram

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low temp low press quartz

alpha qtz

High temp quartz, low press quartz

Beta qtz

Low press high temp silica

Tridymite, Cristobalite

High Pressure Varieties usually found in the dep mantle

Stishovite

High Pressure High Temp quartz associated with meteorite impact

Coesite

F=0

Invariant, only 1 set of TP condition exists and there is no freedom

F=1

Univariant, on the phase boundaries. 1 way only of Freedom as T change P will change and Vice Versa

F=2

Divariant, on Phase Stability Fields, can change T and P invariably without affecting the stability of the system

Plagioclase is an example of

Two Phase Diagram with complete solid solution

Represents the composition of the two phases in equilibrium with each other at that temp

Tie Line

How to know the Albite Anorthite composition of the crystals and Melt in a two component plag system

1) Composition of 100% Solid and Liquid will always be that of the Isopleth or the reference vertical Line 2) Compositions at the melt+crystal stability field can be determined by projecting a horizontal line from the desired temperature of cooling. ?The intersection of the TIE LINE with the liquidus curve represents the melt composition ?The intersection of the TIE LINE with the solidus curve represents the initial crystal composition

This rule states that the proportion of the tie line on the solidus side of the system represent the liquid% while the proportion of the tie line on the liquidus side composition represents Crystal%

Lever Rule

At the liquidus, %liquid is

100%

Diopside-Anorthite is an example of

Binary System with no Solid Solution

Mimum liquidus temp for an anorthite-diopside system, which is the eutectic point

An 42, 1274 deg cel

For 100% solid An 100 the temp is

1553 deg cel

For 100% solid Di100 the temp is

1392 deg cel

For Dio-Anorthite, at what An composition will a melt + Anorthite exist?

>An42

The point at which two liquidus line intersect with the solidus or which represents equilibrium between a liquid and two solids

Eutectic Pt

At eutectic crysallization how much of the crystal is Anorthitic and Diopsidic in composition?

Thru Lever Rule 42% Anorthite 58% Diopsde

what is the final rock composition

%An and %Di Crystals based on the isopleth

Continuous crystallization of Diopside makes the melt what

More anorthitic

Truths based on Two component eutectic systems in terms of crystallizatio and rock formation

1) Which mineral crystalize first depends on the melt composition 2) Separation of crystals to melt generally cause the melt composition to change towards the eutectic 3) Multiple minerals can crystallize simultaneously at the same time

Truths based on Two component eutectic system in terms of Melting and magma generation

1) Composition of first melt is same for a wide variety of system compositions. Always at eutectic 2) degrees of partial melting caused the composition of the melt to change 3) Changes in liquid composition depend on the compsition of crystaly being incorporated in the melt (kaya mas nagiging less anorthitic kasi diopside crystals ang inaadd)

What is invariant melting

Same melt composition but different rocks melted due to influence of degree of partial melting

At this temp, a complete solid solution exists between orthoclase and albite

>670deg cel

This marks the stability fields <670 deg cel where the complete solid soln between ortho and albite has been limited

Miscibility Gap

A phase boundary that separates the conditions under which a complete solid soln is stable from that under which solid soln are limited

Solvus

When is solvus temp the highest?

When both end memers have the highest conc.

unmixing of a complete solid solution to two separate solids

Exsolution

when an initially K-felds rich solid soln the result upon exsolution is

Perthite Plag (K-felds crystals with blebs of Albite)

When an initially Na-Felds rich solid soln exsolves the results will be

Antiperthite Plag (Albite crystals with blebs of Orthoclase)

Convesion of Cristobalite to Tridymite at 1470 is through?

Isothermal Inversion

The intermediate compound between Nepheline and Silica is

Albite

What is the ratio of nepheline and silica to produce albite

1:2

When is a system said to be silica exactly saturated

2/3 Silica%

Evidence for silica oversaturation

Presence of Tridymite, Qtz and Plag

Evidenc for Silica undersaturation

Presence of low silica feldspathoids such as Nepheline

Evidence for Exact Saturation of Silica

Presence of feldspar and absence of both Silica and Feldsphathoids

What kind of phase diagram is silica nepheline

Two side by side eutectic phase diagram One for undersaturated <2/3 % Silica One for Saturated >2/3% Silica

Eutectic of albite and silica

1060 deg cel Si77%

Eutectic of albite and Nepheline

1070 deg cel Si 62%

Intermediate between Forsterite (Mg-Olivine) and Quartz

Enstatie (Mg-Pyroxene)

A reaction where earlier forme minerals react with melt to form different minerals like what occurs between olivine and pyroxene

Discontinuous Reaction

A point on the liquidus line which represents the conditions at which an earlier formed mineral react with melth to form a new mineral

Peritectic Point

Peritectic Point of Olivine-Pyx system

1585 deg cel at 35%Silica

Silica % when the Oli-Pyx system is exactly saturated and all crystals that will be formed at peritectic is Enstatite

Si30%

Forsterite and Feldsphatoid cystallization implies that the system is Silica ___________

undersaturated

When melting of one crystalline material produces both a new crystalline material and a melt of different composition

Incongruent melting

The Eutectic Pt is at

1540 dec cel @46% Silica

Conversion of Forsterite to Enstatie at peritectic is through?

Isothermal Conversion

Diopside and Anorthite

An42 @1274 deg C

Max solvus of Orthoclase and Albite

670 deg

Nepheline Albite

Si62 @1070 deg C

Albite Silica

Si77 @1060 deg C

Inversion of Cristobalite to Tridymite

1470 deg C

Peritectic of Foresterite-Silica

Si 35@1585 deg C

Eutectic of Enstatite -Silcia

Si 46 @ 1540 deg C