Rocks – a rock is a collection of one or more minerals Ms Hartnett's Earth Rock facts Most rocks have a number of minerals in common In other words, only a small number of minerals are very common Most rocks are heterogeneous This means that they are made of two or more different minerals and are not the same throughout Some (very few) rocks are homogeneous or monominerallic This means that they are made of only one type of mineral and they are the same throughout Rocks are divided into major classes They are sedimentary, igneous, and metamorphic Rocks are classified by how they formed or origin Structure, texture, and composition (what a rock is made of) help us to figure out the environment that the rock formed in (origin) Ms Hartnett's Earth Ms Hartnett's Earth Sedimentary Rocks – rocks that formed from the accumulation of deposited rock particles, fragments, and organic material underwater (Remember, they are deposited in horizontal layers)? There are basic categories of sedimentary rocks: Clastic – the rock fragments are lithified (glued) together to form a rock These rocks are made of different pieces stuck together Conglomerate and Breccia have the largest particles Crystalline/Chemical - rocks that formed from ions (smallest particles) that were dissolved in the sea water These rocks usually form as the ocean water evaporates away and leaves the dissolved minerals behind These are also monominerallic Bioclastic/Organic – rocks formed from biologic products (Things that died and solidified together over time Coal and limestone are great examples Ms Hartnett's Earth Ms Hartnett's Earth Igneous Rocks – rocks formed from the cooling and solidification of molten materials (magma) Whenever lava cools, an igneous rock forms There are two sub-classes of igneous rocks: Intrusive/Plutonic – igneous rocks that cooled and solidified beneath the Earth’s surface (The magma cools underground) These rocks take a very long time to cool because they are not on the surface Because they take a longer time to cool, they end up having large crystals/grains Extrusive/Volcanic – igneous rocks that cooled and solidified on the Earth’s surface Lava on the surface cools to form igneous rocks These rocks cool very quickly and have very small crystals/grains or none at all (glass) Ms Hartnett's Earth Ms Hartnett's Earth Metamorphic Rocks – rocks that have been changed by the action of heat and pressure from occurrences inside the Earth Metamorphic rocks were once sedimentary, igneous, or a different type of metamorphic rock Because of the heat and pressure of magma coming in contact with rock, the former rock changes into a new one The rock does not melt while it changes into a metamorphic, but it almost does It just deforms and distorts What kind of rock would form if rock melted and then re-cooled? There are two groups of metamorphic rocks: Foliated – alignment of minerals in paper thin layers or bands Non-foliated – no alignment of minerals Ms Hartnett's Earth Ms Hartnett's Earth