of a Melt lbite (NaAlSi Os; abbrevia albite (NaAl Question 3 -Phase Diagrams: Co
ID: 286649 • Letter: O
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of a Melt lbite (NaAlSi Os; abbrevia albite (NaAl Question 3 -Phase Diagrams: Coolin for e cooling of a melt using the solid solution T-X phase diagram side of the x-axis, and calcic plagioclase anorthite (CaAlzSi2Os uler for your estimations and measurements.) some plagioclase mineral s shown below. The sodic plagioclasea abbreviated An") is shown on the right side of the x-aios and measurements.) Note: you'll likely want to use a r 1600 1553 500 uidus 1400 PLAGIOCLASE L 1300 200 PLAGIOCLASE CRYSTALS 1118 1100 0 Ab 60 80 20 40 100 An WEIGHT PERCENT An a. We're going to start with a hot melt (T-1500°C) composed of 30% An. At approximately what temperature will you observe the first crystals forming from the melt? What will be the composition of those first crystals?Explanation / Answer
The given figure is showing Albite-Anorthite complete solid solution phase diagram.
a.The crystallisation of melt starts at 15000C with 30% An component. The first crystal will form when the melt touches the liquidus curve at approximately 13900C. At that position the composition of cystal will be Ab30An70 (determined by extrapolating the line on the solidus curve and then vertically downwards on the x-axis).
b. When the temperature is lowered graduallly, the liquid will move along the liquidus curve and the crystallization of albite proportion will increase. At 13000C, the composition of the crystal will be approximately Ab50An50.
c. Applying the Lever rule, the proportion of solid at 13000 C, ax/ab = 10/ (10+20) = 33.33%
The proportion of liquid composition, bx/ab = 20/(10+20) = 66.67%
d. At 13000 C, the percentages of albite and anorthite will be 50%.
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