Igneous Rocks PDF

SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Igneous Rocks By the end of this lesson, I will be able cl...

SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Igneous Rocks By the end of this lesson, I will be able classify different types of igneous rocks based on their physical characteristics and formation Recall that a rock is defined as a naturally formed group of minerals that are bound together. Igneous rocks are formed from the crystallization of magma. Igneous means born of fire. The location of the cooling magma determines the rate at which it cools which, in turn, determines the texture of the resulting rock. Intrusive Igneous Rocks Intrusive igneous rocks form deep beneath Earth’s surface. The elevated temperatures associated with deep burial allow the magma to remain liquid for an extended period of time. The slow cooling allows more time for the atoms within the magma to freely move about forming large crystals. This gives these rocks their characteristic coarse-grain texture. These rocks appear on Earth’s surface when they are uplifted, and the overlying rock is worn away. Extrusive Igneous Rocks Extrusive igneous rocks form when the magma reaches Earth’s surface (lava) and quickly cools. The rapid crystallization that occurs results in the formation of microscopic crystals. These rocks are said to have a fine-grain texture. Magma Types The type of magma from which the igneous rock forms determines the colouring of the resulting rock. ​ Felsic magma contains large amounts of silica, SiO2. It is thick, slow to move and slow to rise. When it crystallizes it produces a rock light in colour. Granite belongs to this family of rocks. ​ Mafic magma contains little silica. It is hotter, thinner and more fluid. When cooled it produces a dark and dense rock. ​ Intermediate magma, as its name suggests, contains moderate amounts of silica and as a result has a viscosity in between that of felsic and mafic magma. When cooled a rock of medium grays and green are created. SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Therefore we end up with 6 different families of igneous rock Magma is a slushy mix of molten rock (liquid), gasses, and mineral crystals (solid). Different minerals have different melting/freezing points. As the magma cools, the minerals with the highest melting points are first to crystallize. As the temperature drops, these crystals react with other elements in the magma forming new crystals. In this way minerals evolve in predictable patterns. Silica and oxygen, the most abundant components of magma, have the lowest melting points and are therefore last to crystallize forming quartz. As a result, quartz veins are common because this last liquid portion of the magma is often squeezed into rock fractures. The interlocking grains within igneous rocks make them especially strong. Because of this, they are useful as building materials. Many ore deposits can be found within igneous rock formations these include platinum, chromium, nickel, and gold. Surrounding igneous intrusions can be found gold, silver, lead and copper. SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Igneous Intrusions Volcanoes only provide a hint at magma activity below Earth’s surface. Forces deep within Earth push magma into fractures within bedrock which are classified based on their formation and resulting structure. These igneous intrusions are often referred to as plutons. As indicated in the diagram, dikes and sills are sheets of magma intruded into previously formed rock. A dike spans vertically, while a sill spans horizontally. These structures are common in regions of volcanic activity. Some magmas are stiff and do not flow easily. Instead of spreading into sheets, these magmas bulge upward to form domed masses known as laccoliths. The rock layers above a laccolith are also pushed upwards to form domed structures. These structures can be found in the Henry mountains of Utah. Once an inactive volcano erodes, it can leave behind the solidified magma, aptly named a volcanic neck. This is the central plug of the previously existing volcano. Batholiths, the largest of all plutons, form the cores of many of Earth’s mountain ranges. They are usually made of granite or granodiorite and can span tens of thousands of square kilometers. Batholiths are also exposed through erosion and uplift of overlying rock layers. The largest batholith in North America forms the core of the coast range of southern Alaska and British Columbia, Canada. SES4U​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Name: ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ Date: Practice! 1.​ Create a venn diagram that compares similarities and differences of felsic and mafic magmas. 2.​ Why do igneous rocks have different textures? 3.​ What causes magma to form a laccolith instead of a sill? 4.​ Which rock, obsidian or gabbro would make a better cutting tool? Why? 5.​ A sample of magma is observed to flow very easily. Would you expect it to contain high or low amounts of silica? Why?