8.1 Igneous Rocks Flashcards
What are igneous rocks?
Igneous rocks - Rocks formed from cooling magma and lava are known as igneous rocks. Rocks formed at the surface from lava cooling are known as extrusive igneous rocks. Rocks formed by cooling magma are intrusive igneous rocks.
What are crystals and how do they form?
Crystals -When magma is solidifying, particles in the liquid rock may clump together to form structures called crystals. When magma cools quickly it forms rocks with very small crystals or no crystals at all. Magma that cools slowly gives the crystal plenty of time to grow so the form big crystals.
What are minerals?
Minerals - Rocks are made up of minerals. Minerals are chemical substances with combinations and arrangements of atoms that can be identified by their physical properties. Two physical properties of minerals are their size and shape of the crystals that form in them.
What is, and how to classify igneous rocks?
Classifying igneous rocks - To classify a rock geologist, need to examine the texture. Texture describes whether the rock is smooth or has obvious grains, lumps, air bubbles or interlocking crystals in it. You can also use colour to classify igneous rocks. Colour is linked to the minerals in the rock. Dark coloured rocks have heavy minerals such as olivine a green mineral. Olivin contains heavy minerals like iron. So the rock cooled quickly so they are extrusive igneous rocks. Lighter coloured rocks have lighter colour minerals and had more time to cool and form so they are intrusive igneous rocks.
What are extrusive igneous rocks?
Extrusive igneous rocks – have very small crystals in them. Many extrusive rocks have holes or spaces in them. These are caused by gas bubbles trapped when magma cools very quickly.
What are intrusive igneous rocks?
Intrusive igneous rocks – contain large crystals which can usually be seen without a microscope. These crystals are the result of magma cooling slowly. The crystals also interlock.
