Question 2 of 7: Mineral & Rock Identification

Question 2: Mineral & Rock Identification (20 marks)

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.

(a) (i) Gypsum – hardness 2 on the Mohs scale (can be scratched by a fingernail). (ii) Galena – perfect cubic cleavage in three directions at 90°. (iii) Hematite – reddish-brown streak (diagnostic even though the hand specimen may look metallic black-grey). (iv) Potassium feldspar (orthoclase) – typically pink to flesh-coloured (also cream/white/light tan). (v) Garnet – vitreous to sub-resinous luster.

(b) (i) Diamond – native element (carbon). (ii) Malachite – carbonate (basic copper carbonate). (iii) Pyrite – sulfide (iron sulfide, FeS₂). (iv) Sylvite – halide (potassium chloride, KCl). (v) Apatite – phosphate (calcium phosphate).

(c) (i) Dark, glassy, quickly-quenched silica-rich lava — obsidian. (ii) Biochemical rock of altered plant remains — coal. (iii) Fissile, mud-sized clastic rock — shale. (iv) Hard, non-foliated contact-metamorphic rock — hornfels. (v) Foliated, glossy, mica-rich metamorphic rock — schist (mica schist).

(d) (i) Arkose – detrital (feldspar-rich clastic sandstone). (ii) Graywacke – detrital (poorly-sorted, clastic sandstone with a muddy matrix). (iii) Chert – chemical (biochemical/chemical silica precipitate). (iv) Breccia – detrital (clastic, angular fragments). (v) Rock salt (halite) – chemical (evaporite).