Neco 2019 Geography Question 6

A field geologist examined an outcrop on the northern flank of the Jos Plateau. The following observations were recorded: - The rock is coarse‑grained, visibly crystalline, and composed mainly of quartz, feldspar, and biotite. - The texture is phaneritic with interlocking mineral grains. - The rock exhibits a porphyritic texture where large feldspar phenocrysts are set in a finer groundmass. - No obvious layering or foliation is present. - The outcrop is associated with a network of dykes composed of fine‑grained dark rock. Answer the following: a) Identify the type of rock described and justify your identification using the observed mineralogical and textural features. b) Explain the geological processes that led to the formation of this rock, including the role of magma cooling rate and tectonic setting. c) Discuss two economic uses of this rock type in Nigeria, citing specific examples.