So, the places on Tiamat’s body where she was pierced by the chain anchors of her Allagan bindings have “bled” purple crystals.
Consider the implications of this. Consider the purple crystal formations all over the Delta Quadrant around her.
From the moogle quests in the area, we also know that Tharl Oom Khash was home to Ratatoskr’s brood. Combined with the information from this sightseeing log entry, there is a heavy implication that the location is where the Knights Twelve, led by Thordan, killed Ratatoskr.
The Aery, too, is covered in similar purple crystals. Though Nidhogg wasn’t killed, he was badly wounded and left for dead when the Knights took his eyes, and Tiamat shows that a dragon needn’t be fully dead to “bleed” crystal- a solidified form of their aether. For that matter, Midgardsormr shows that. Just as Nidhogg survived certain death in dormancy, so did he- in the middle of a wasteland blanketed in crystals caused by his own fall. It wasn’t the ceruleum exploding that made all of the crystals in Mor Dhona- they’re Midgardsormr’s aether, a considerably more vast quantity.
The corrupted crystal formations from the Calamity were also the leavings of dying dragon, admittedly in primal form.