Formation of Igneous Rocks
Igneous rocks are constituted of magma which has crystallized and solidified becoming a rock. There are two distinctive categories- extrusive and intrusive, which have different features due to their different environments. Intrusive igneous rocks are formed in conditions of extreme heat and pressure within the mantle of the earth. They gradually crystallize over a period of several millennia within the magma, and due to these conditions they have large crystals of isolated minerals which are present within the rock structure. Extrusive igneous rocks are formed from magma violently ejected from a volcano during an eruption which crystallize faster due to their colder conditions and form smaller crystals. It is possible for a rock to partially crystallize intrusively but then be forced to the surface before the process was complete therefore the rock would be a combination of large and small crystals.
Structure of Igneous rocks
Igneous rocks contain crystals of isolated minerals within the rock structure. Intrusive Rocks have larger crystals than extrusive rocks but generally they have the same fundamental structure: crystals of minerals arranged in a completely random pattern within the rock. They are basically a rock formed out of crystals. In intrusive igneous rocks such as granite the individual crystals are clearly visible; in extrusive rocks they may not be visible to the naked eye and within the third category, of rocks such as obsidian, the crystals are so minuscule that the rock has a glass like surface and may be referred to as volcanic glass. The different appearances of the rocks are caused by the different interactions of the elements and compounds within the magma influenced by the surroundings and the type of magma.
How do Igneous Rocks differ from other Rocks
Igneous Rocks are completely different from other rocks due to their utterly different formation process. They crystallize into a random arrangement of interlocking crystals of minerals such as quartz whereas the other rocks have bands, or are foliated. Igneous rocks are never foliated as within the magma the crystals are not in conditions that cause them to be arranged into layers and instead they crystallize at different levels of speed due to their different chemical properties, therefore the rocks are arranged into crystals of minerals randomly position and interlocking with each other with no opportunities for them to become foliated.
Examples of Igneous Rocks
Granite: Granite is a very common intrusive igneous rock with large, clearly visible crystals, very large due to the slow crystallization, formed of varying minerals. It is extremely hard and considered relatively and therefore useful for buildings and construction projects, and work surfaces within homes and other workplaces.
Obsidian: Obsidian is an extrusive igneous rock which is relatively common. It is black and translucent, with a glass-like surface, it is sometimes referred to as volcanic glass. Obsidian is brittle and when broken leaves extremely sharp edges making it useful for weapons such as swords and arrows. Obsidian is also attractive due to its shiny surface so is used for decorations, it also has some mythological and magical connections.
Rhyolite: Rhyolite is an extrusive igneous rock which has quite large crystals formed of minerals including quartz. It has a similar chemical composition to granite so it resembles it in some aspects, although is less common. It is used for both decoration and practicalities.
Dolerite: Dolerite is an extrusive igneous rock with minscule crystals which are less than 1mm in of minerals including olivine and quartz. It can also be referred to as diabase or microgabbro. It is used as crushed stone and for ornamental purposes.
Pumice: Pumice is an extrusive igneous rock with large bubbles. These bubbles are formed due to swift cooling and depressurization when the rock is ejected from the volcano, as gases emerge within the rock but then are immediately trapped causing the unusual texture of pumice. The colors of pumice vary from light and yellow to dark grey and due to its texture it is useful for cosmetic and exfoliating purposes.
Igneous rocks are constituted of magma which has crystallized and solidified becoming a rock. There are two distinctive categories- extrusive and intrusive, which have different features due to their different environments. Intrusive igneous rocks are formed in conditions of extreme heat and pressure within the mantle of the earth. They gradually crystallize over a period of several millennia within the magma, and due to these conditions they have large crystals of isolated minerals which are present within the rock structure. Extrusive igneous rocks are formed from magma violently ejected from a volcano during an eruption which crystallize faster due to their colder conditions and form smaller crystals. It is possible for a rock to partially crystallize intrusively but then be forced to the surface before the process was complete therefore the rock would be a combination of large and small crystals.
Structure of Igneous rocks
Igneous rocks contain crystals of isolated minerals within the rock structure. Intrusive Rocks have larger crystals than extrusive rocks but generally they have the same fundamental structure: crystals of minerals arranged in a completely random pattern within the rock. They are basically a rock formed out of crystals. In intrusive igneous rocks such as granite the individual crystals are clearly visible; in extrusive rocks they may not be visible to the naked eye and within the third category, of rocks such as obsidian, the crystals are so minuscule that the rock has a glass like surface and may be referred to as volcanic glass. The different appearances of the rocks are caused by the different interactions of the elements and compounds within the magma influenced by the surroundings and the type of magma.
How do Igneous Rocks differ from other Rocks
Igneous Rocks are completely different from other rocks due to their utterly different formation process. They crystallize into a random arrangement of interlocking crystals of minerals such as quartz whereas the other rocks have bands, or are foliated. Igneous rocks are never foliated as within the magma the crystals are not in conditions that cause them to be arranged into layers and instead they crystallize at different levels of speed due to their different chemical properties, therefore the rocks are arranged into crystals of minerals randomly position and interlocking with each other with no opportunities for them to become foliated.
Examples of Igneous Rocks
Granite: Granite is a very common intrusive igneous rock with large, clearly visible crystals, very large due to the slow crystallization, formed of varying minerals. It is extremely hard and considered relatively and therefore useful for buildings and construction projects, and work surfaces within homes and other workplaces.
Obsidian: Obsidian is an extrusive igneous rock which is relatively common. It is black and translucent, with a glass-like surface, it is sometimes referred to as volcanic glass. Obsidian is brittle and when broken leaves extremely sharp edges making it useful for weapons such as swords and arrows. Obsidian is also attractive due to its shiny surface so is used for decorations, it also has some mythological and magical connections.
Rhyolite: Rhyolite is an extrusive igneous rock which has quite large crystals formed of minerals including quartz. It has a similar chemical composition to granite so it resembles it in some aspects, although is less common. It is used for both decoration and practicalities.
Dolerite: Dolerite is an extrusive igneous rock with minscule crystals which are less than 1mm in of minerals including olivine and quartz. It can also be referred to as diabase or microgabbro. It is used as crushed stone and for ornamental purposes.
Pumice: Pumice is an extrusive igneous rock with large bubbles. These bubbles are formed due to swift cooling and depressurization when the rock is ejected from the volcano, as gases emerge within the rock but then are immediately trapped causing the unusual texture of pumice. The colors of pumice vary from light and yellow to dark grey and due to its texture it is useful for cosmetic and exfoliating purposes.
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Extrusive igneous rocks are formed
by magma cooling quickly when
ejected from volcanoes in their
eruptions.
by magma cooling quickly when
ejected from volcanoes in their
eruptions.