18-Geol-A1 Mineralogy and Petrology · December 2018
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 18-Geol-A1 Mineralogy and Petrology, 2018-Dec. Closed book; no calculator permitted.
Reference texts: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (silicate/oxide structural classification, mineral chemistry and formulas, crystal systems); Winter, Principles of Igneous and Metamorphic Petrology, 2nd ed. (magmatic differentiation, Bowen's reaction series, metamorphic agents/facies, volcanic and pyroclastic processes, partial melting); Boggs, Petrology of Sedimentary Rocks, 2nd ed. (carbonate mineral diagnostics).
Question text not reproduced: the examination questions are © Engineers and Geoscientists BC. Open the official past paper (linked at the top of this page) to read the question, then follow the worked solution below.
All five metals form simple or spinel-group oxides under conditions too oxidizing (or, for U, too reducing) to stabilize a sulfide instead; each has one dominant, diagnostic oxide mineral used in the field and in ore assessment.
| Metal | Mineral | Formula | Notes |
|---|---|---|---|
| Iron (Fe) | Magnetite | $\text{Fe}_3\text{O}_4$ | Isometric spinel-group oxide, strongly magnetic; forms in igneous, metamorphic and BIF settings alongside hematite ($\text{Fe}_2\text{O}_3$). |
| Chromium (Cr) | Chromite | $\text{FeCr}_2\text{O}_4$ | The only economically important Cr ore mineral; a spinel-group oxide concentrated by early crystallization/settling in layered mafic–ultramafic intrusions (e.g. Bushveld). |
| Titanium (Ti) | Ilmenite | $\text{FeTiO}_3$ | Rhombohedral (hematite-structure) oxide; the dominant primary Ti ore, commonly intergrown with magnetite as exsolution lamellae. |
| Uranium (U) | Uraninite | $\text{UO}_2$ | Isometric; the principal U ore mineral, stable only under reducing conditions (readily oxidizes/alters to secondary U6+ minerals near surface). |
| Copper (Cu) | Cuprite | $\text{Cu}_2\text{O}$ | Isometric Cu(I) oxide; a secondary/supergene mineral formed by oxidation of primary Cu sulfides in the oxidized cap of a porphyry or vein deposit. |
