Starstones were very very dense and heavy, and they grew extremely hot when used.
They could be found or used when the seeker enters a state of deep meditation and calmness, appearing as a beacon in the darkness.
Starstones possess an energy field unlike any on Earth, having the ability to do things that are impossible without them.
Upon their introduction, a starstone was used to power the Soraxians' spaceship, allowing Elgar and Kirana to first land on Earth and make contact with Evangeline. This ability is remarkable and demonstrates the tremendous energy potential of a Starstone. Considering the vast expanses of space between the center of the Milky Way - where Sorax is located - and Earth on the outer edge of the Orion Arm, a starstone should be able to deliver a very powerful and steady stream of energy capable of powering a ship through interstellar flight. The starstone that pulled the spaceship through was also small enough for Evangeline to handle personally, which means that such a small object was capable of such massive feats.
Even before Evangeline found the Starstone, it was being 'used' to heal the sick humans on the island that it had landed on. This healing power of the Starstone is possibly its most remarkable characteristic, and this power would prove invaluable in the future.
When Elgar and Kirana were very badly hurt in an attack from a bear, Evangeline put a used and nearly depleted Starstone between their incapacitated bodies and brought them 'back to life.' Whether or not the Starstone actually performed revival or merely restored energy to them is unclear.
Starstones 'respond' to danger, demonstrated by Evangeline's superhuman abilities while she was about to be killed for heresy and witchcraft. Because the starstone was not calibrated to benefit humans as they do the Soraxians, Evangeline was granted abilities that severely strained her muscles and body and almost killed her.
Starstones have been used to channel interstellar communications and give off a form of radiation exceeding in power even gamma-ray or cosmic radiation, as detected by the USS Dakota and the Hei Ten Shi. This radiation has the unique characteristic to disable or cause machinery to malfunction mysteriously, leading to the demise of the Hei Ten Shi and also the sluggishness of the controls on the USS Dakota. More ominously, starstone radiation could also overload immortal cells and cause mental instability, eventually leading to death.
Starstone energy is used to perpetuate Immortal lifespans.