Stage 3 Revision Metamorphic Rocks

Metamorphic Revision Rock Cycle 3 R’s Types of Metamorphism Regional Contact Dynamic Metasomatic Metamorphic Grades Increasing with Pressure/Temperature

Index Minerals The presence of certain minerals in a Metamorphic rock tells you the temp and the pressure it was formed at Many of these minerals are only present in Metamorphic rocks Some of these minerals are Polymorphs A polymorph is a compound that has differing atomic structures eg Diamond/Graphite

Polymorphs Mineral crystallisation occurs under specific conditions. Diamonds exist under the crust where the pressure and temps are very great, and must be brought up fast (in a volcano) too slow and they will turn into Graphite

Al2SiO5 The best index mineral in Metamorphic rocks. Kyanite Sillimanite Andalusite

These minerals are all made from the same elements/compound Al2SiO5 But they only form at certain temperatures The presence of any tells you the approximate temp and pressure the rock formed at.

Metamorphic Textures Pressure causing alignment of minerals Sheet like texture called Foliation Increased grain size Due to incresed temperatures and pressure for a longer period

Texture - Foliation Here you have minerals growing in a preferred orientation in the rock. Some layers are thin others are thick. Foliation can give a rock a striped or streaky appearance Foliated rocks are distinguished by their grain size and nature of the foliation. Minerals such as Muscovite (Mica) and Chlorite

Slate The finest grained foliated rock Parent rock (Protolith) Shale, Mudstone LOW grade metamorphism (what does this mean?) The rock has a slaty CLEAVAGE in one direction. That comes from the pressure above and below the rock. Minerals: Chlorite Clay or Mica (Muscovite) Quartz* Feldspar* * In smaller amounts

Phyllite Fine grained Parent rock: Slate Names after the greek for leaf because the rock has a leafy lustre. Minerals: Mica Chlorite Feldspar* Quartz* * in smaller amounts

Schist Medium to Coarse grained rock Schistocity: Preferred orientation of larger Mica crystals (than Phyllite) caused by stress (from the pressure that would have caused the metamorphism) Also the formation of wavy or distorted surfaces instead of flat planes Forms at a higher temp than Phyllite Minerals: Kyanite Feldspar Quartz Amphibole Garnet (Sometimes as a Porphyroblast/clast)

Gneiss Coarse grained Alternating layers of dark and light coloured minerals Gneissic texture, high grade metamorphism Banding, Banding can occur for different reasons Temperature causing minerals to grow in bands Sheering helping the minerals grow in bands Minerals Quartz Biotite Garnet Feldspar Sillimanite

Other textures Lineation Banding Augen Minerals grow as prismatic crystals facing a similar direction Banding As mentioned previously Augen Quartz and similar silica minerals can be squashed into an ellipsoid shape (eye)

Other textures Granular Folding This is important! All mineral grains in a metamorpic rock are approximately the SAME SIZE. Because they have been exposed to the same pressure/temp for the same time. These occur in rocks with a simple chemistry (eg Sandstone SiO2 and Limestone CaCO3) These are generally NOT foliated but have had high temps! Folding Directional pressure can make rocks behave plastic Now for these types (and the others) what types of metamorphism could they be related to?

Non Foliated Here the crystals have grown without anything restricting their growth (or making them grow in a preferred orientation) Often formed without any pressure-only temp The crystals are interlocking Often made of only one mineral

Hornfels Parent rock: Shale, mudstone, limestone Fine grained Minerals: Dependent on Parent rock (can differ) Shale or clay hornfels are made of Biotite but have Andalusite and Sillimanite in it. What does that say about its formation location?

Quatrzite Parent rock: Sandstone Original loose SiO2 grains that have recrystallised making larger and interlocking formation. Minerals: SiO2 (Quartz)

Marble Parent rock: Limestione Original loose CaCO3 grains that have recrystallised making larger and interlocking formation. All fossils destroyed Mineral: CaCO3 (Calcium Carbonate or Calcite)

Metamorphic Grade As pressure and/or temperature increases so does the amount of change a metamorphic rock makes. This is the Grade

Metamorphic Grade As the Metamorphic Grade increases the minerals in the rock changes as well. They change in a predictable pattern depending on Pressure and Temperature.

Metamorphic Facies These are a set of metamorphic mineral assemblages (or ingredients) that relate to a certain range of pressure or temperature

Metamorphic Resources Industrial Talc Graphite Garnet Asbestos Kyanite, Andalusite & Sillimanite Building Slate Marble Quartzite Gneiss