According to the guide, the most valuable amethysts are those that are categorized as medium reddish purple with a slight tint of brown.. This rare amethyst commanded between $64.00 and $70.00 as of March 2014. At the same time, the least valuable amethysts were those that were very light purple in color.
Geology and Sources of Energy. by Steve Sharp, P.E. Some of our mineral resources can be taken out of the ground and used for fuel. Raw materials have two sources: they can be grown or they can be mined. Coal, oil and gas are collectively called fossil fuels, because they formed from organic (living) matter. Uranium is also a source of energy that is taken out of the ground. These fuels that are mined are called non-renewable resources, because we can't replace them.
   So essentially, all fossil fuels are considered non-renewable.   Fossil fuels are considered nonrenewable resources because, fossils  fuels are made from the remains of dead plants or animals. It takes  more than a million years for the fuels to form from the fossils. It is a long process. ossil fuels (coal, oil and natural gas) are non-renewable. They took millions and millions of years to form and are being used up in a time scale of hundreds of years. When they are gone, it will take millions of years again for the processes that create coal and oil to happen.