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19 Cards in this Set

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Basalt
This is an extrusive igneous rock that is low in silica. It usually forms at the mid-ocean ridge, or in Hawaiian volcanoes.
Pumice (Basalt)
When lava has a lot of trapped gas, it can cool with bubbles in it, forming pumice. This is also extrusive.
Obsidian
This is an extrusive rock that is high in silica (similar to rhyolite or granite) but it cooled so quickly that it has no separate crystals or grains. It is also called "volcanic glass."
Granite
This is an intrusive rock that makes up most of the continental crust. It cooled slowly underground and has formed many separate crystals or grains of silica and other minerals.
Porphyry
This is a bad picture. The porphyry we saw in class was darker. It has two sizes of crystals because it cooled slowly at first, making large grains. Then something happened so that the rest cooled quickly with small grains. It is intrusive.
Detrital Limestone
This is clastic and organic. It formed from shells of sea-creatures. It has the same basic elements as regular limestone, but it is clastic instead of chemical.
Sandstone
This is clastic. It is made from layers of different colored sand. Good geologists can look at the sand grains and tell whether the sand was deposited by wind or by water.
Mudstone
This is clastic, but the grains are smaller than the grains in sandstone. Mudstone usually forms in wet areas with slow moving water, like a lake.
Shale
Shale is also clastic, but the grains are so small that they are like clay. It is very smooth, with sometimes visible layers. It forms in very still ponds or oceans where tiny particles settle to the botto
Limestone
Limestone is a chemical rock. It forms at the bottom of the ocean, as dissolved carbon and calcium accumulate molecule-by-molecule, like a crystal. The limestone in class has some fossils in it.
Chalk
Chalk is a type of limestone, that has more calcium and fewer other minerals.
Volcanic Breccia
This rock is sometimes considered Igneous, because it forms from the ash and cinders that erupt in an explosive eruption, from a pyroclastic flow. It is clastic.
Quartzite
This forms from sandstone, under heat and pressure, but not enough to become foliated. The quartzite in class is more pink in color.
Marble
This forms from lighter colored limestone or chalk. Black marble comes from dark limestone. It is not foliated.
Marble Breccia
Marble breccia forms from volcanic breccia, but I couldn't find a good picture. Look at the one in class.
Slate
Slate forms from shale. It is like natural pottery. It is foliated by the heat and pressure into layers that make it good for tiles.
Mica (Really pretty but fragile)
Mica is very foliated. It can come from any rock that is very high in silica. It is like natural glass, and it was called "isinglass" in the past.
Gneiss
Pronounced "nice." Gneiss forms from granite that experiences more heat and pressure. It is foliated.
Schist (think of manhattan)
Manhattan is made out of schist. It is foliated. Schist can form from many types of rock. It comes from mudstones, or from basalt or granite too. It forms after a lot of heat and pressure, more than is necessary to make slate. It can be hard to tell what original rock the schist is from.