22. Minerals and Igneous Rocks

Photo 38: The Fairmont Hotel Macdonald, with exterior cladding consisting of  Indiana limestone. Edmonton, Alberta. 2011-05-10

Minerals and Rocks

Minerals are crystalline in nature, which means that the atoms are orderly arranged. This arrangement is best seen with microscopes and X-rays; however, some crystals are naturally beautiful like diamonds. Minerals are inorganic compounds found in rock, in fact, the mineral structure is molten rock which has hardened over a long period of time underneath the Earth. Lava that comes to the surface and cools down quickly becomes rock that does not have the orderly crystalline structure. Obsidian is an example of rapidly cooled lava. Rocks and Minerals are defined by their properties in: chemical composition, hardness, cleavage/fracture, colour/streak, and lustre. Almost 75% of all rocks in the Earth’s crust are made up of Silicon and oxygen. Other common elements are Aluminum, Iron, Calcium, Sodium, Potassium, and Magnesium.

Igneous Rocks

There are 3 types of rocks: Igneous rock, formed by cooled magma; sedimentary rock (photo 38), formed by weathered igneous rock which is eroded, transported, and deposited; and metamorphic rock, which is igneous rock transformed by heat and/or pressure. Igneous means in Latin ‘born of fire.’ Intrusive igneous rocks are hardened lava in the crust; extrusive igneous rocks are hardened lava on the crust. Granite (photo 39) is an intrusive igneous rock. The larger the crystals in the intrusive rock, the slower the cooling process. These rocks with large crystals are called plutonic igneous rocks.

Photo 39: Black granite exterior surface, former building of the Imperial Bank of Canada, Edmonton, Alberta. 2011-05-10