The one on top left is organic shale/sandstone sometimes found mixed with coal, it will burn, but leave a lot of ash as your pic of it partially burned has told you. The piece on the bottom left looks like a clinker. If your furnace is making clinkers try using less underfire air, if you have a fan that feeds the fire when it calls for heat, this could be your problem; reduce the air intake on the fan to lower the speed and volume of air flowing through the fuelbed, this will bring down the fuel bed temp and eliminate clinkering. Is the coal you're using producing white, tan, pink, or orange/red ash? there's not much I can tell you about the coal pieces on the right - to tell you anything about unburned coal from a picture you're going to have to give me a VERY high resolution pic, having said that, if I was to guess, i'd say the top right is organic shale high in iron and pyrite and the stuff on the bottom right is lighter weight and more pure coal.