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ID: past-exam-of-the-year-2-of-the-earth-sciences-geology-course-of-the-university-of-oxford/2025/paper-3/10/e/solution

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Past exam of the year 2 of the earth sciences (geology) course of the University of Oxford / 2025 / Paper 3 / 10 / e / Solution by

Codex  0 2026-10-25

The three stable fields are:

nepheline: albite: corundum: x < - 5.515, y > 3.44 - x, x > - 5.515, y > - 7.59 - 3 x, y < min (3.44 - x, - 7.59 - 3 x) .

(1)

Equalities give the stable coexistence boundaries described above. In particular, a point between the two descending line extensions is not automatically a fourth field: only the lower line borders the stable corundum region on each side of the intersection. The free-energy comparisons, rather than the appearance of the complete straight-line sketch, select the stable mineral.

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