Classification based upon formation Rock types Classification based upon formation

Igneous rocks form from molten lava. What’s the difference between magma and lava? The formation of igneous rocks is destructive because old rocks are melted and constructive because new rocks are formed.

Igneous rocks When magma cools slowly while still under ground, the minerals in the rock have time to form crystals. Those crystals make intrusive igneous rocks have a coarse grain with visibly mottled coloration. Granite is a coarse grained intrusive rock made mostly of quartz

Other intrusive igneous rocks Peridotite is a coarse-grained igneous rock made mostly of olivine Diorite is a coarse grained igneous rock made mostly of feldspar

EXTRUSIVE IGNEOUS ROCKS When lava cools on the Earth’s surface, there is little time for crystals to form, so extrusive igneous rocks lack the coarse grain typical of intrusive igneous rocks. Basalt is a fine-grained extrusive igneous rock, which happens to be the most common rock on Earth. It is susceptible to chemical weathering, where it breaks down to form clay.

Extrusive igneous rocks Obsidian is volcanic glass which cools so rapidly that not even the finest crystals can form.

extrusive Igneous Rocks Scoria is another igneous rock filled with vesicles – the proper term for the gas bubbles in these rocks. Pumice cools so quickly and with so many gas bubbles that it can float.

Metamorphic Rocks Metamorphic rocks have been modified by heat, pressure and chemical process usually while buried deep below Earth's surface. Exposure to these extreme conditions has altered the mineralogy, texture and chemical composition of the rocks. Marble is an nonfoliated metamorphic rock which forms when limestone is exposed to great heat and pressure.

Metamorphic rocks Both slate (below) and gneiss (at right) are examples of foliated metamorphic rocks . Foliated metamorphic rocks have obvious layers and often split into thin sheets.

Sedimentary Rocks Sedimentary rocks form from the accumulation of sediments, often but not always at the bottom of a body of water. Sedimentary rocks are divided into three major groups: clastic, chemical, and organic. Conglomerate is a clastic sedimentary rock, which means it forms as a result of mechanical weathering.

Clastic Sedimentary rocks Sandstone and shale are both clastic sedimentary rocks. Sandstone is made of compressed particles of sand, and shale is made of smaller particles of clay or mud.

Halite is rock salt which forms when Chemical Sedimentary Halite is rock salt which forms when bodies of salt water evaporate, leaving their salt content behind. Hematite is iron ore that formed when the iron and oxygen in bodies of water chemically reacted and settled to the sea floor.

Organic Sedimentary Rocks Coal forms from the remains of decayed plant matter in swampy environments. Limestone forms from the accumulation of calcium-rich shells, coral and other detritus of marine life

How is the water cycle vital to the formation of sedimentary rocks? In what ways is the formation of sedimentary rocks both constructive and destructive? How is the water cycle vital to the formation of sedimentary rocks?