At any point along cotectic, Di crystallizes along with plagioclase of intermediate composition.Ī. One cotectic line descends continuously from Di-An eutectic temperature to Di-Ab eutectic temperature. Ab-An side is solid solution loop - no minimum. Di-An and Di-Ab sides represent binary eutectic systems - generates cotectic line in ternary diagram One or more sides represent solid solution binary systems (no binary eutectic) Peritectic point in binary diagram becomes a reaction curve in ternary: in 3D diagram, cotectic lines ~ valleys reaction curve ~ inflection point (change in slope)Ī. Recall enstatite melts incongruently to Fo + liquid System forsterite-silica-anorthite - binary compound - incongruent melting Components Ne-Tr-Di: albite forms between Ne and Tr line joining Ab and Di separates equilateral triangle into 2 separate triangular diagrams.Ĭ. System nepheline-silica-diopside - congruent melting - binary compound. 3 cotectic lines intersect at ternary eutectic point = lowest melting temperatureī. Adding the 3rd component to each side lowers the temperature below the binary eutectic. Binary eutectics along each side => 3 cotectic lines. Simplest ternary diagram: each side represents a binary eutectic system: liquidus lines become surfaces eutectic points become cotectic lines a ternary eutectic forms where the 3 liquidus surfaces intersect arrows show direction of decreasing temperature At Y along XA, composition is: %A = XY/XA %(B+C) = YA/XA (but B/C = XC/BX, so %B = (XC/BC)*(YA/XA)/%C = (BX/BC)*(YA/XA) If A is added, ratio B and C doesn''t change => composition lies along line XA Along side BC, A=0: let X be along side BC. Note: this holds even if the triangle is not equilateral. Any point in the interior of the triangle = mixture of all 3 Any point on AB = mixture of A and B, no C Representation by an equilateral triangle System albite-anorthite-diopside-forsteriteĪ. System nepheline-silica-diopside - congruent melting - binary compound Phase Diagrams with More Than Two ComponentsĪdd 3rd dimension: temperature.
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