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Beginners Guide to Geology
This guide is aimed at beginners in the study of geology which is the study of the origin, history and structure of the Earth, and for anyone interested in minerals and gemstones, like me, is a must to take up either as a hobby or a career. To understand how minerals are formed, it is necessary to have a basic grounding in geology, to be able to recognise the types of rocks and the crystals formed millions of years ago within.
In each different type of rock are different crystals, depending on the chemical elements contained within the rocks.
The Earth is entirely made up of elements and minerals which are mixtures of elements.
There are 90 known elements, as laid out on the Periodic Table of Elements that you may remember from science classes at school.
At the present time, there are 3,700 known minerals, with new discoveries each and every year as scientific equipment gets better.
Our world is made up of rocks, molten or otherwise. From where we stand on the surface of the earth, there is a massive 10 miles of solid bedrock below us. Contained within this are minerals.
These 10 miles (the distance is shallower in the depth of the oceans) are called the crust.
Below the crust is the mantle. The mantle is 1,800 miles deep. The deeper you go, the hotter the bedrock becomes.
Below the mantle is the 3,000 mile outer core which is made of molten rock, consisting of mostly iron and nickel.
At the inner core it is reckoned to be solid rock once again, with a depth of 900 miles. It is believed to be made up of mostly iron, with a little nickel thrown in.
There is 4000 miles between where you are standing and the centre of the Earth.
The planet is millions of years old. There are various scientific theories as to how the Earth formed, and no-one knows for certain. The Big Bang Theory sounds the most plausible.
However, it is generally accepted that the Earth formed 4½ billion years ago (4,600,000,000) and that at the time of forming it was super hot.
We know there have been several Ice Ages since then and all have shaped the Earth as we know it.
Volcanoes push molten lava out from the outer core through weaknesses in the Earth’s mantle causing mountain ranges to form, while glaciers change the shape of whole mountains.
Shifts in the tectonic plates of the world have also moved continents and land masses to where they are today. The existence of tectonic plates is a modern day theory to explain this phenomenon.
There are reckoned to be 8 large tectonic plates.
· North American
· South American
And many various smaller ones
· Juan de Fuca
· And more
Scientific tests have proven that they are all moving, very slowly and at various rates. Over the millions of years the Earth has been in existence they may have re-organised themselves many times. The tectonic plates sit on the surface of the Earth’s mantle.
Where they move away from each other, molten rock, called magma, from the mantle may escape through, and this may form new mountain ranges, or new islands or land masses when it occurs at sea. This is where strong volcanic activity is present.
When they move towards each other, they cause earthquakes, which as we all know are devastating to life on the Earth’s surface.
On these giant tectonic plates lie many fissures and faults, which cause weaknesses within the plates. These are known as fault lines, along which earthquakes periodically occur.
Rocks are made up of three types
Sedimentary rock is the youngest type of rock, and is the type that has been carried along on river beds, or swept down mountains by glacial activity. The effects of wind and water erosion swept this rock off the old bedrock or extrusive rock (rocks that we can see – mountains etc) and over a period of several million (or even 1000s) years, compaction of this gravel, or old vegetation and other waste matter turned to solid rock.
Igneous rock is the oldest type of rock on Earth. Formed as the name suggests, from fire, igneous rock is solidified molten magma, and is widespread throughout the planet, proof of our fiery-hot beginnings. 95% of the earth’s crust is made up of igneous rock.
Metamorphic rock is, as its name suggests, rock that has
been changed. Heat and pressure deep under the Earth’s surface has mixed igneous rock with sedimentary rock
and the result is metamorphic rock, within which are found many of the world’s
minerals and crystals.