Whatever it’s origins, Runestone is the key to magic in the world. Physically, it is a lackluster gray; it is slightly porous and lightly gritty to the touch. It is very difficult to grind any significant powder off with ones hands, but a small hammer, chisel or a suitably dense material can easily grind the stone down to nothing in short order. The stone breaks down very evenly into a uniform powder.
Ingestion of the Stone is a very rare trait. The one hereditary consistency seems to be that the children of Magi (or a Magi to a non-Magi) has never been able to consume the stone. It usually takes a few generations for another Stone Eater to show up in a family tree. Thus, all current Magi were born of families that could not cast. There is no line of succession, no favorites in the Order due to birth.
Runestone can be eaten or snorted. Orally consuming the stone is the most preferred method since it is easy to gauge, comfortable and more gradually metabolized by the body. Olfactory consumption allows the power of the Stone to enter the control of the Magi much quicker but there is a price – coming down from the does is very quick and harsh and can leave a Magi drained. Additionally, it is difficult to tell exactly how much Stone has been consumed, so overdose can be an issue. Alternatively, some Magi claim it is best absorbed directly into the bloodstream (say, by cutting oneself and rubbing stone in the wound) but this is not considered wise practice. At the pyreneums there are said to be chambers where Runestone is burned like incense, its dense smoke filling the air. The levels of Stone in the air would be fatal to mundane folk, and unbearable and unhealthy to all but the most aged Magi. Most Magi eat the stone, reserving olfactory ingestion for emergencies and quick recharges. On the subject of overdose: The stone itself is only lightly addictive. The more one uses it, the more one becomes accustom to the heightened sense and power it brings. Regular consumption of the stone is necessary to avoid withdraw symptoms – fever, chills, weakness, nausea – but this need only be small amounts (≈ 1oz./2-3 days) to avoid symptoms. Dominus and Arch Magi, are known to keep bowls of the stuff near them at all times, snorted or eating small handfuls throughout the day. This is not only mind-expanding, but incredible expensive. As rare as it is, overdose does occur from time to time. The results vary from Arch Magi Alwyn destructive rage that nearly destroyed Three Gates in 355 AI, to Wandering Wodin Bronwyn’s complete disappearance from the world (along with the surrounding acreage) during the Carver Rebellion of 701 AI.
When the stone is given to non-Magi the results are devastating. Seemingly insignificant amounts cause sickness and occasionally death. Hallucinations are common. In large amounts, it is a fast acting poison, killing within minutes. Just the right amount, however, can be very useful. A carefully administered dosage of Runestone makes the unlucky victim into a mindless slave, completely lacking in willpower. He will carry out orders without emotion and is completely subject to any spells cast on him.
(images were taken and modified from this site)