Trivia: It seems to me
, one of the companies used to coat their coal with something to make it blue.
Edit: Found it
Glen Alden Coal
In the heyday of Anthracite mining in Pennsylvania, many of the coal companies branded their coal. This was done as a sales gimmick. One of the most famous branded coals was the Glen Alden Coal Company's "Blue Coal" . Often the coal was dyed a color other than black. This dye also served as a lubricant to allow the coal to travel down chutes and bins more easily. When the coal traveled more smoothly, it was less likely to break into smaller pieces. Catchy slogans came with the brand names.