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.
Types of Biomass Fuels. Biomass fuels are organic materials produced in a renewable manner. Two categories of biomass fuels, woody fuels and animal wastes, comprise the vast majority of available biomass fuels. Municipal solid waste (MSW) is also a source of biomass fuel.Biomass fuels have low energy densities compared to fossil fuels.ifferent types of woody fuels can typically be mixed together as a common fuel, although differing moisture content and chemical makeup can affect the overall conversion rate or efficiency of a biomass project. There are at least six subgroups of woody fuels.