What are these "clinkers" that are left behind in the fireplace? Answered
"Clinkers" is the word my dad came up with for them, because they make a glassy "clink" when you drop them. They aren't like regular embers, they're much denser, and they look kind of like coprolites made of particle board. Can't tell you what kind of wood makes them, because we use various types and they show up unpredictably.