15/12/2009 - Rocks are created by the fire or heat from erupting volcanoes.
IGNEOUS ROCK
These are made from fire or heat from erupting volcanoes.
Obsidian is nature’s glass, formed when lava from a volcano cools quickly on the surface.
Pumice is full of air pockets that were trapped when the lava cooled.
It is the only rock that floats.
There are 5 kinds of igneous rocks, depending on the mix of minerals in the rocks.
Granite: this contains quartz, feldspar & mica
Diorite: Are a combination of feldspar & one or more dark mineral. Feldspar is dominant.
Gabbro: also contains feldspar & one or more dark mineral. The dark minerals are dominant.
Periodotite: contains iron and is black or dark.
SEDIMENTARY ROCKS
Like the Rocky Mountains on the west coast of North America, all mountains are tall and jagged when first formed. Over millions of years mountains become old like the Appalachian Mountains on the east coast of Canada and the United States. This leaves them much rounder and rocks get worn by erosion. Eventually, smaller partd of the original mountain find their way to streams and rivers becoming sediments of rock.
This happens all the time, layer after layer of sediments of rock building up over time in layers like pages of a book slowly creating a story. These are Sedimentary rocks. Some examples of sedimentary rocks are sandstone and shale and you will often find fossil in theses sedimentary rock deposits from plants and animals that have died over the years.
Carbon can be produced when large amount of plant become fossilized and this gives us coal, oil, natural gas, and petroleum.
Sedimentary rocks cover 75% of the earth’s surface and there are 6 main kinds of sedimentary rocks depending on the appearance of the rock.
Conglomerate rock (pebbles, boulders)
Sandstone is a soft stone that is made when sand grains cement together
Shale is clay that has been hardened and turned into rock.
Limestone is a rock that contains many fossils and is made of calcium carbonate &/or microscopic shells.
Gypsum, common salt or Epsom salt is found where sea water precipitates the salt as the water evaporates.
Breccia has jagged bits of rock cemented together in a matrix.
METAMORPHIC ROCKS
Metamorphic rocks This word comes from the Greek word Meta and Morph, put them together and they become metamorphic meaning changing form. Due to movement in the earth’s crust, Igneous and Sedimentary rock becomes metamorphic rock.
Marble is one such rock that began life as Sedimentary rock. The earth’s crust moved and crushed the Sedimentary rock so hard and with added heat that it forced the change to take place. Marble is basically transformed limestone.
Foliated metamorphic rocks have banding, or layers.
Slate is shale that has transformed. Slate splits into smooth slabs
Schist is probably one of the most common metamorphic rocks. Mica is the most common mineral.
Gneiss has a streaky look that is due to its alternating layers of minerals.
Non-foliated metamorphic rocks are not layered.
Quartzite like Marble is very hard and is very popular in kitchens.
EROSION
Being a key player the rock cycle, erosion is responsible the formation of some very interesting landscapes. People who live in such areas will over years have an effect on the slowing down or speeding up this process. However, the main cause for erosion is the weather: i.e.: rain, temperature, and the wind etc. the rain is what hits the hardest when it comes down as acid rain. It’s not just rain fall though, but the rivers and streams that are kept alive and running. Other effects on rocks are how hard or soft the minerals are and the plant life surrounding the area and even the soil that has already been formed from years previous will have a chemical reaction with newly fallen rocks.
GEMSTONES
Gemstones are often what are being described when we talk about "crystals". There are many gemstones and most are used for jewelry or decoration. Few minerals that are found in nature are suitable to use unaltered for jewelry.
One exception is the "Herkimer Diamond", which form in vugs of gray rock Herkimer, New York. These may not be real diamonds as they are in fact quartz crystals that look like diamonds because they have been cut and polished but they are just as beautiful.
