I agree with EnergyNumbers. A few more points on coal however: the value and investment can vary slightly depending on the region of the world you are on. Australia still as significant interest in coal with several mines in place and new mines being planned, such as Adani. Coal investments, here in Australia, are under extreme pressure from environmental groups and citizens in general.
China and Australia still have a high interest in coal, due to existing investments which will last 10-20 years more. The energy plants in Australia are mostly coal based, and the steel production in China uses coal extensively (currently). Even in Australia, though, the end of the coal era is discussed already.
The major use of coal is energy (through burning it). There are other uses, but I don't think these could sustain the industry as it is now - the demand would be much smaller. For possible uses, check here: https://www.worldcoal.org/coal/uses-coal
Finally, ethically you shouldn't invest in Coal. Looking at ethical or sustainable funds do not have coal industries in their portfolios.