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.
Problems with fossil fuels. Burning fossil fuels â gas, coal, oil and more recently shale gas â are considered the most economic ways to generate electricity. Fossil fuel however, is a finite resource, the cost of which increases sharply as the availability decreases.oal is the dirtiest method of producing energy and is responsible for a lot of the chemical pollution we hear about in China and India. The simple truth is that we are overly-dependent on fossil fuels and need more non-fossil fuel derived power to ensure security of supply over the coming decades.