Grade 6 Science Unit 09 Lesson 02 The Process of Forming Metamorphic Rock The term metamorphic comes from the following Greek terms meta change and morph form Therefore metamorphism means to change form Metamorphic rocks are found in the Earth s continental crust The process of metamorphism does not completely melt the rocks but changes them into other rocks which are denser and more compact It can take millions of years to form metamorphic rocks At extremely hot temperatures the crystal structures of the minerals that make up the rock are broken down By using different combinations of the available elements and compounds in the rock new minerals are created Buried rocks are under a huge amount of pressure because of the weight of sediments and rocks above them Pressure can also be exerted on rocks due to the forces of tectonic processes The most obvious effect of pressure on rocks is the reorientation changing direction of mineral crystals Below are some examples of existing rocks and the metamorphic rock that they may become Sedimentary Metamorphic Igneous Limestone changes to marble Phyllite changes to schist Granite can change into gneiss Sandstone changes to quartzite Schist changes to gneiss Basalt changes to greenstone Shale changes to slate Recrystallization occurs as the particle size of the rock changes during the process of metamorphism In order for the process of recrystallization to occur both high temperatures and pressures must be present Crystals in metamorphic rock may not always be visible without the use of a microscope Textures of metamorphic rocks are separated into two categories foliated and non foliated Foliated rock is caused by uneven pressure that deforms the rock making it appear to have stripes The pressure is greater in one direction than another The uneven pressure causes the minerals in the original rock to rearrange in one plane This will reduce the overall pressure on the rock and give it a striped look Slate is an example of foliated rock Non foliated rock is formed in areas of high temperatures and low pressure The pressure is equal from all sides This rock does not appear to have stripes but the combination of high temperatures and low pressure causes the minerals in the original rock to recrystallize into larger sizes The atoms become more tightly packed together and this increases the density of the rock Quartzsite is an example 2012 TESCCC 05 23 13 page 1 of 1
Grade 6 Science Unit  09 Lesson  02  The Process of Forming Metamorphic Rock The term metamorphic comes from the following...