THE STUDY OF ROCKS. HOW ROCKS ARE FORMED.
HOW ROCKS ARE FORMED
THE EARTH'S CRUSTThe whole earth is made of rocks & minerals. Inside the earth there is a liquid core of molten rock and on the outside there is a hard crust. If you compare the earth to an egg, the shell on an egg is like the crust on the earth. The crust is made up of rocks and minerals. Much of the crust is covered by water, sand, soil and ice. If you dig deep enough, you will always hit rocks. Below the loose layer of soil, sand & crumbled rocks found on Earth is bedrock, which is a solid rock
The Crust makes up less than 1% of the Earth’s mass (0.4%) It is made of oxygen, magnesium aluminum, silicon calcium, sodium potassium, iron. There are 8 elements that make up 99% of the Earth’s crust. The continents are about 35 km thick and the ocean floors are about 7 lm thick.
The Mantle is the solid casing of the Earth and is about 2900 km thick. It makes up about 70% of the Earth’s mass (68.1%). It is made up of silicon, oxygen, aluminum and iron.
The Core is mainly made of iron and nickel and makes up about 30% of the Earth’s mass (31.5%). The Outer Core is 2200 km thick and is liquid and the Inner core is 1270 km thick and is solid.
A mineral is composed of the same substance throughout. If you were to cut a mineral sample, it would look the same throughout. There are about 3000 different minerals in the world. Minerals are made of chemicals - either a single chemical or a combination of chemicals. There are 103 known chemical elements. Minerals are sorted into 8 groups. Some common examples have been listed for each.
Native Elements ~ copper, silver, gold, nickel-iron, graphite, diamond
Sulfides ~ sphalerite, chalcopyrite, galena, pyrite
Halides ~ halite, fluorite
Oxides & Hydroxides ~ corundum, hematite
Nitrates, Carbonates, Borates ~ calcite, dolomite, malachite
Sulfates, Chromates, Molybdates, Tungstates ~ celestite, barite, gypsum
Phosphates, Arsenates, Vanadates ~ apatite, turquoise
Silicates ~ quartz, almandine garnet, topaz, jadeite, talc, biotite mica
When rocks break down into smaller & smaller pieces, they turn into sand. If you look at the sand under a microscope, you will see that sand is made up of the same minerals as the rocks that the sand came from. When plants start to sprout up in sand, it is turning from being just small bits of rock to being soil.
Rocks are constantly being formed, worn down and then formed again. This is known as the Rock Cycle. It is like the water cycle but it takes a lot longer. It takes thousands and millions of years for rocks to change. Rocks are divided into 3 Types. They are classified by how they were formed.
Some good sites that help explain this are:
The Stupid Page of Rocks Describes metamorphic, sedimentary & igneous rocks
Rocks and the Rock Cycle A well written description of the Rock Cycle.