The sun-shard was a large and mysterious crystal sought and desired by multiple entities during the history. It was just a bit smaller than a troll, by size.
As other similar crystals, it appears to contain voices that can get in contact with beings close it. It glowed of own multiple lights, moving on the surface (or inside?) the crystal on their own.
AuRon is believed to have been positively helped by the presence of the crystal while studying and reading scrolls close it, Wistala was affected on the same way: she noted that when she moved away from the crystal, the effect vanished. However Wistala also realized that the crystal had some negative effects, increasing her frustration, and learned of travelers who were brought to madness after too much exposure. She also believed to have seen dragons (in the shapes and lights into the crystals) but also a large tower (possibly the Anklamere tower?).
Blighters claim the shard was the "living heart" of their ancient empire, having come from the sky, and having helped the blighters to build their civilization. It was said to have been stolen by Anklamere, and helped him to subject the charioteers, but later retrieved by NooMoahk during the War of the Sorcerer and returned in Old Oldam.
Demen also claim to have been the first owner of the sun-shard: Paskinix account however match the blighters' one stating that it "fell to earth" in Lavadome and it was there collected by a demen.
Both the accounts seems to confirm that the craft reached the earth from outer space: it's unknown if such fall occurred previously or alongside the coming of Anklemare (however it appears it occurred previously, even if the link between the being and the shard appears confirmed).
NooMoahk never revealed it, but it's hinted that he placed himself as guardian of the sun-shard, possibly to prevent other beings to use the secret powers (or to prevent it affecting other beings?).
After his death, the blighters (and especially the group of Fireblades) swore to protect the sun-shard, fighting successfully the demen during the First Battle for the sun-shard, and then the Ghioz Empire during the Second Battle for the sun-shard.
However it was lost to them, when the Ghioz Empire used dragon mercenaries during the Third Battle for the sun-shard.
After the War of the Red Queen, the sun-shard come in possessions of dragons: it was brought into the Lavadome and there was studied by Rayg for many years. It become clear the connection with the Lavadome (structure) itself, and Rayg realized how it was actually some kind of engine: one of the two other pieces that are needed to activate the Lavadome itself (in addition with the crystal staff).