Power Stones are a powerful magical tool. They connect a spell caster to the power of remote Ley Lines and Ley Line Nexii. It may also be possible, where such things exist, to connect to a Clathrate.
Unused Power Stones appear as two orbs of stone connected by a thin neck, like an hourglass. The maker carves it from a single cylindrical piece of rare stone. Once shaped, each half is the size of a hen’s egg. The next step is to inscribe the entire surface with mystical runes. This process takes several weeks of effort by an expert.
To use, the user brings the connected stones to the chosen ley line, nexus or other power source. The user should prepare a defended place to hide the source stone.
All that remains is to break the two halves apart and place the source piece. The remaining stone is ready for use.
The stone now allows its bearer to draw upon magic as if they were standing at the source stone’s location. If someone moves the source stone, this severs the magic connection.
This item assumes that rules for using Ley lines exist in your game. Where such rules are not present, here are some suggestions:
Ley lines are 'natural' sources of power for magic. They allow the caster to draw power instead of using their own personal reserves. Game masters could allow this energy to augment spells, increasing power or 'casting level'. For Manna-based systems, these stone provide a supply of running manna.
You may choose that a user must have a specific skill to use these stones, or spend time attuning it.
Options & Ideas
Value of Stone
The power and nature of the manna provided by the stone could vary with the quality of the stones used. Perhaps different minerals have affinities for different types of magic.
This is How they do Magic Here
In this world, the only way wizards can cast spells is to use these stones. Each stone requires a unique magical place for the source stone. Wizards can carry many stones, and greater levels of power need greater levels of skill to use.
With few exceptions, wizards use only those stones they had crafted and placed themselves.
The party has found one of these stones. It seems quite potent. Unfortunately, the Ley line it draws from is variable. Occasionally, surges of different types of magic can erupt, causing an unexpected dark taint to magic.