User blog comment:M'aiq the Lover/Origin behind Ash Spawn/@comment-26474238-20131031185328

That second point of yours is speculation. The only confirmed fact behind Heart Stones is that they were flung across Solstheim after the eruption of Red Mountain. And with the magical properties seen within Red Mount during the events of TES: Morrowind, it's not hard to believe that Heart Stones were just natural mineral deposits natural to such an environment.

As for the Ash Spawn... I don't seem to recall any established lore behind them. I suppose they're just another magical entity similar to wisps.