18-Geol-A1 Mineralogy and Petrology · December 2017
Nivaar worked solution (AI-drafted; not reviewed by a licensed engineer)
EGBC National Exam — Geological Engineering, 04-Geol-A1 Mineralogy and Petrology, 2017-Dec. Closed book; no calculator permitted. Part 1 requires all five 10-mark short-answer questions (50 marks); Part 2's page-1 header says "5 of the 8" while the page-3 instructions say "5 of the 7" and list exactly 7 questions (a source discrepancy noted on the exam page itself).
Reference texts: Klein & Dutrow, Manual of Mineral Science, 23rd ed. (silicate/sulfide/carbonate structural classification, mineral chemistry and formulas); Winter, Principles of Igneous and Metamorphic Petrology, 2nd ed. (magmatic differentiation, metamorphic agents/facies, volcanic processes, layered intrusions and cumulates, partial melting, ophiolites); 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.
| Agent | What it does | Geological example |
|---|---|---|
| Heat (temperature) | Drives mineral reactions and recrystallization toward higher-T stable assemblages; the primary control on metamorphic grade. | Thermal aureole around a shallow granitic pluton, producing a zoned sequence of hornfels facies outward from the contact. |
| Pressure (confining/lithostatic) | Uniform, all-sided pressure from overlying rock load; increases density and favours smaller-molar-volume assemblages without imposing preferred orientation. | Burial metamorphism at the base of a thick sedimentary basin (zeolite/prehnite–pumpellyite-facies burial diagenesis). |
| Differential stress | Unequal stress in different directions; drives dynamic recrystallization and preferred mineral alignment, producing foliation/lineation. | Schistose fabric developed in a ductile shear zone at a convergent-margin fold-and-thrust belt (regional dynamothermal metamorphism). |
| Chemically active fluids | Aqueous/carbonic fluids transport heat and dissolved species, catalyzing reaction rates and enabling metasomatic (allochemical) mass transfer. | Skarn formation at an intrusion–limestone contact, where fluid-borne Si, Fe, Al and Mg are exchanged for country-rock Ca. |
