|“||Take it, and cut your brother's throat with it, and take back the honor of your blood.||”|
Said to be the length of a forearm, Heosphoros is half the size of Phaesphoros. It is described as beautiful and is made of black gold and adamas. The cross-guard, grip, and pommel are gold with obsidian, and the blade is a silver so dark that it looks nearly black. On the other side of the blade, along the center ridge, is a pattern of black stars, symbolizing the Morgensterns.
While in Clary's possession in 2007, it was kept in a dark leather scabbard with a pattern of silver stars sewn through it.
Heosphoros was made by Wayland the Smith many years ago when the Morgenstern family commissioned two new blades for a father and his son. Of the pair, Heosphoros was the smaller one, having been designed for the son. The two blades were named after different aspects of the morning star, after which the Morgenstern family was named, with Heosphoros meaning "dawn-bringer."
In the days before the Dark War, Clary Fairchild, along with Jace Herondale, visited Diana's shop in search of a new weapon. Knowing that the sword would never be bought by anyone else, as it hadn't been after over a decade, Diana offered to give Clary Heosphoros for free. When Clary initially showed reluctance toward owning something associated with her father's family, Diana advised her to kill her brother with it and avenge her family's good name and honor.
In Edom, Jace unleashed his heavenly fire upon the realm. With a vision of a rune Clary had been receiving from Ithuriel for some time, Clary was able to contain the heavenly fire within Heosphoros. The heavenly fire momentarily infused in the sword and disappeared once Clary used it to stab and kill Sebastian Morgenstern.