(excerpted from Jacob Miller's Collectible Cosmos, Volume XXXIX)
Thunder Eggs are ovoids of a hard, brittle, opaline crystal, usually between ten and fifteen centimetres in length. The crystal from which the Eggs were shaped reacts to light, temperature, and magnetic flux to display endless kaleidoscopic patterns of refraction within its depths. It has, thus far, resisted any attempts to synthesize, and it has no known industrial use.
They were the prized possessions of the Katchelli Egg Men of Khassandhra, Waddall's Star IV, who believed that their mana was intimately caught up in them. A Katchelli who defeated another would would take and display the egg of his fallen foe, eventually giving it to the children of the tribe to play with. The loser lost face and status until he could mine and shape another egg for himself, when he might once again take his place among the lowest of the warriors - the "Young Eggs". The egg of the victor, however, gained in stature with each victory. The eggs were usually passed down through the generations, and only if there was no worthy warrior son to bequeath it to would a Katchelli be buried with his egg.
The loss of an egg in battle was shameful, but acceptable. An egg lost or destroyed by accident, however, was an irredeemable disaster. A warrior who received such evidence of the hatred of the gods would often simply waste away and die, or roam the Katchelli settlements in a berserk trance until killed.
To steal an egg, even that of a reviled enemy, was a crime so revolting to the Katchelli that it was virtually unimaginable. Such a criminal would be put to death in a protracted and exquisitely painful manner. Though the days of the Great Eggs are long past, the descendents of the Katchelli Egg Men still venerate the memory of their mighty ancestors and the Eggs which hold their souls. As a result, collection of Thunder Eggs is neccessarily a furtive business, and one which is undertaken only by the most adventurous of collectors.