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.
Fossil fuels are an incredibly dense form of energy, and they took millions of years to become so. And when theyâre gone, theyâre gone pretty much forever. Itâs only a matter of time. There are three different types of fossil fuels â oil, gas and coal. Clearly, our reserves of these are finite - it's a matter of when they run out - not if.