When pre-existing rocks change form while remaining solid. Metamorphic Rocks When pre-existing rocks change form while remaining solid.

Question… The word metamorphose means “to change form.” What are some ways that you can think of that things change?

Remember the Rock Cycle? How many different kinds of rocks can become metamorphic?

How does metamorphism happen? As depth increases, pressure and temperature increase. When temperature and pressure become high enough, rocks melt and form magma – but what if the rocks do not reach the melting point? If the rocks do not melt, but the high temperature and pressure combine to change the texture or composition of a rock without melting it, a metamorphic rock forms.

Where does this heat and pressure come from? High temperatures come from Earth’s internal heat. High pressure comes from deep burial or from compression during mountain building.

So, how can minerals change without melting? When temperature and pressure change, minerals go through “solid state alterations” to change into new minerals that are stable at the new temperature and pressure. Scientists can even look at a rock and tell what the conditions were during its formation, just by looking at the minerals present!

Classified by Texture Metamorphic rocks are divided into two categories: Foliated and Non-Foliated.

Foliated Rocks Foliated rocks have layers and bands of minerals. SLATE SCHIST GNEISS Foliated rocks have layers and bands of minerals. High pressure causes crystals to form perpendicular to the pressure. SO – if pressure is coming from top and bottom, bands will be horizontal.

Non-Foliated Rocks In these rocks, minerals form with blocky crystal shapes. Quartzite and marble are common examples. DID YOU KNOW – Marble forms from limestone? QUARTZITE MARBLE

Types of Metamorphism We can look for clues about what type of metamorphism occurred by looking at… the minerals that form the degree of change in rocks

There are THREE types of metamorphism: Regional metamorphism Contact metamorphism Hydrothermal metamorphism Each type results from heat coming from a different source!

Regional Metamorphism This happens when large regions of the crust are affected. Can result in changes in minerals and rock types. Can result in folding and deforming of the rock layers.

Contact metamorphism When molten material comes into contact with a solid rock. High temperature, moderate to low pressure. Different minerals form at different distances from the heat.

Hydrothermal Metamorphism When very hot water reacts with rock and alters its chemical and mineral composition. Hot fluids move in and out of the rock, causing mineral composition and texture to change. This is how valuable ore deposits are formed.

So, why are metamorphic rocks important? Metamorphic rocks are used in construction. Marble Slate MANY mineral resources come from metamorphic rocks! Metal ores – native gold, silver, and copper Iron ores – magnetite, hematite Talc Asbestos Graphite

So, how is it all connected? REMEMBER ME???

The Rock Cycle Metamorphic rocks form when other rocks change. Rocks are grouped into the three categories by how they form. Most rocks will not always stay the same. ANY rock can be changed into ANY OTHER type of rock!