METAMORPHIC ROCKS

1. METAMORPHIC ROCKS Rocks of Change

2. The Keys to Metamorphic Rocks • Remember, “metamorphism” literally means to change form • But what changes about the original parent rock? • The size, the shape, the texture, and even the chemistry of the minerals can change! • Which kind of rocks can be changed into a metamorphic rock? All Types: • Igneous rocks can be changed • Sedimentary rocks can be changed • Even metamorphic rocks can be changed into other kinds of metamorphic rocks

3. Meta-why? • What is it that can cause these rocks to change so drastically? • Three factors: • Pressure from deep burial • Heat from deep burial or a nearby magma body • Chemically active fluids percolating through the rock (we don’t get into this)

4. Meta-how much? • Do all rocks get changed the same amount or the same way? • No: It’s a sliding scale, much like many other things in geology • Low-grademetamorphism • hardly changed from the original parent rock • High-grademetamorphism • cannot even recognize the original parent rock The hotter and deeper the rocks go the greater the metamorphism will be

5. Different types of Change • There are 3 types of metamorphism: • Burial Metamorphism • Contact Metamorphism • Regional Metamorphism

6. Burial Metamorphism • Burial Metamorphism – usually a low grade change due to pressure caused by shallow to medium burial; heat is not a major factor Burial Metamorphism will not drastically change the parent rock

7. Contact Metamorphism • Contact Metamorphism – also usually a low grade change; the parent rock comes in contact with a magma body and gets cooked enough to metamorphose Contact Metamorphism Rising magma bodies will metamorphose nearby rocks

8. Regional Metamorphism • Regional Metamorphism – both heat and pressure change rock on a grandscale; this usually occurs during major tectonic events such as mountain building Regional Metamorphism The highest grade of change will occur during regional metamorphism

9. Texture You Say? • The texture of a metamorphic rock can be classified • But unlike an igneous rock, there are only 2 types of texture • Foliated Texture • Non-Foliated Texture

10. Foliated Texture • In Foliated rocks mineral grains align parallel because of the pressure & heat • This recrystallized mineral alignment causes the rock to have a banded look • Rocks with multiple mineral types will exhibit this texture Notice the foliation of this gneiss sample

11. Non-Foliated Texture • In Non-Foliated rocks the minerals do not line up parallel • These rocks have a uniform appearance and no banding • Rocks that have only one kind of mineral will usually exhibit this metamorphic texture No mineral alignment Non-Foliated rocks do not have banding in them

12. Naming & Classifying Metamorphic Rocks • We can group these into the two categories based upon the types of texture the rocks exhibit • Foliated Rocks • Slate • Schist • Gneiss • Non-Foliated Rocks • Marble • Quartzite • Anthracite

13. Naming Foliated Rocks • Slate – a low grade metamorphism of the parent rock shale • The thin platy mica flakes line up and give the rock foliation • Slate has great “rock cleavage” and it used as roof & floor tile, chalkboards, and billiard table tops Slate is a low grade metamorphic rock which was once used as hand held chalk boards in schools

14. Naming Foliated Rocks • Schist – higher grade metamorphism of the rock slate • Schist is “platy” due to the mica minerals, and it can be split into flakes & slabs • Schist is a high grade metamorphic change Schist is a high grade metamorphic rock with obvious foliation

15. Naming Foliated Rocks • Gneiss (“nice”) – A foliated rock from the parent rock granite • Minerals are banded, but instead of being platy like schist, they are granular and rounded • Gneiss is a very high grade metamorphic change Notice the good foliation in this sample of gneiss

16. Naming Non-Foliated Rocks • Marble – coarse grained crystalline rock from the parent rock limestone • It has large crystals of interlocking calcite • Calcite has a hardness of 3 so it is relatively soft and great for carving and sculpting • Marble is a low-med metamorphic change New reduced price! It’s Jesus!!! The calcite crystals that make up limestone do not change drastically when marble is made; if anything, they will grow in size as they fuse together

17. Naming Non-Foliated Rocks • Quartzite – very hard rock made from the parent rock sandstone • With heat/pressure the quartz grains simply fuse together • Quartzite is a medium-high grade metamorphic change The rock quartzite is not too different than a large quartz crystal

18. Naming Non-Foliated Rocks • Anthracite – the highest grade of coal • It forms from the continued cooking of bituminous coal • Anthracite is a high grade metamorphism, it is extremely hard, and it burns almost completely clean Both of these anthracite samples are hard and shiny

19. Naming Metamorphic Rocks

20. All aspects of a rock can change during metamorphism All rock types can undergo metamorphism Heat, pressure, and fluids do the changing There are three types of metamorphism: burial, contact, & regional There are two types of textures in metamorphic rocks: foliated & non-foliated Foliated rocks look banded due to mineral alignment Non-foliated rocks do not look banded Learn the six rocks! To Review: