GCE Geography 2024 Theory — Question 4

Model answer

(a) An igneous rock is a type of rock that forms from the cooling and solidification of magma. Igneous rocks can form beneath the earth's surface as intrusive (plutonic) rocks or on the surface as extrusive (volcanic) rocks. Common examples include granite (intrusive) and basalt (extrusive). (b) Three characteristics of igneous rocks: - They can have a range of textures (from coarse-grained to fine-grained/glassy, depending on cooling rate). - They can be hard (e.g. granite, basalt) or soft (e.g. pumice, obsidian). - They rarely contain fossils, since they form from molten material. (c) Economic importance of igneous rocks: i. Building materials: Igneous rocks like granite, basalt and andesite are used as building and construction materials (e.g. for walls, kerbs, road aggregate). ii. Source of valuable minerals: They are sources of valuable minerals such as gold, diamonds and other precious metals/gems associated with igneous activity. iii. Manufacturing: They are used in the production of cement, concrete, glass and ceramics. iv. Decorative and ornamental use: Igneous rocks like granite, marble-like polished basalt and obsidian are used for decorative purposes, such as countertops, sculptures and jewelry. v. Cosmetics and skincare: Igneous rocks like obsidian and pumice are used in cosmetics, such as exfoliating scrubs and skincare products. vi. Scientific research: They are used in scientific research to study the earth's geological history and volcanic activity. vii. Water filtration: Igneous rocks like zeolites are used for water filtration and purification. viii. Construction of highways: Igneous rocks like basalt and andesite are used in highway construction due to their strength and durability.