Neco Model Questions Vol1 2020 Geography Question 6

Practice essay / theory question 6 from the 2020 Neco Model Questions Vol1 Geography examination. This question covers Igneous rocks, Rock texture, Petrology, Tectonic settings .

Neco Model Questions Vol1 2020 Geography Essay / Theory

Topics: Igneous rocks Rock texture Petrology Tectonic settings

Question 6 NECO_MODEL_QUESTIONS_VOL1 • 2020 • GEOGRAPHY • essay

A geologist collected a hand specimen of an igneous rock and recorded the following observations: 1. The rock has a coarse‑grained texture. 2. Visible minerals are quartz, feldspar and biotite. 3. The overall colour of the rock is dark grey. 4. It contains phenocrysts of feldspar up to 5 mm in length. 5. The rock exhibits a porphyritic texture (large crystals embedded in a finer‑grained groundmass).

Question Parts

( a )

Identify the rock type and give a brief justification based on the observations.

( b )

Explain the cooling history that produced the observed porphyritic texture.

( c )

Discuss the most likely tectonic setting in which such a rock would form.

( d )

A powdered sample of the rock reacts vigorously with dilute hydrochloric acid, producing bubbles. Explain what this observation reveals about the rock’s mineral composition and how it supports your identification in part (a).

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About This Question

This is Neco Model Questions Vol1 2020 Geography Question 6. It is one of the essay questions from the 2020 Neco Model Questions Vol1 Geography examination.

The question covers Igneous rocks, Rock texture, Petrology, Tectonic settings .

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