The powerstone's are my magical grounding for the series.  They are traditional  magic powerstones in some ways, but they add magic in a daily but subtle way, and provide an underlying, unifying magic principal that links the continents, other planets, and the past and future, opening doors for universal themes, trips to other planets, and the reincarnation story line.

The basic principal is easy.  Using the powerstones, individuals can do what they already do well even better, beynd any human parameters.  Tapping them requires talent and skill.  The better practicitioners are at tapping powerstones, the more they can accomplish.

The stones are mined in a raw form, then refined and transformed by mages.  They are expensive and limited in quality.  The higher the quality, the more expensive.  In this way they are special economic commodity, and tied to both class issues (poor individuals and societies, like the giants and oblins, have limited access), and national politics, as nations fight for access to high quality stockpiles.

The stnes can only be refined by mages, adding a special role of magery and a special talent. One of Davis's special traits is that he is an enchanter, a special title for someone who can make powerstones.  He is extremely good at it, with a higher level of success than most enchanters, and creating higher quality of stones.  When working with other mages, he can create permanently powered objects.  He can do permanent light ones, and working with other mages, combine his power stones with their spells.

Davis's ability to create powerstones allows him to develop some economic independence from his family wealth, by creating stones he can sell fo his own funds.  This is important when he becomes more independent in his early travels, and when he give Kyrene to his sister, and loses that funding for DH.  Then he needs the funds from selling stones to help pay the bills.  Eventually they will find a powerstone mine on DH island, which will secure the island economy.

The powerstones also play a cultural role.  Each nation and culture uses them for power purposes, but also uses them for different cultural purposes.  The orcs use them as tribal artifacts, records of the history and heritage of the tribe.  Humans use them as jewelry, and signs of status and wealth.  Elves use them as personal icons, and symbols of their union with nature.  Dwarves use them as the basis of actual wealth (think of gold as the old money standard).  Goblins use the tiniest, most flawed, cheap, practically just shards, as family totems (think asian house gods).  Giants use them as foundations in their communities.

For magic, doing magic takes a lot of energy.  Someone doing magic just using their own energy can only do a few basic spells before exhausting themselves.  Any extensive/powerful magic requires the use of powerstones.  Magery skill is then based on two factors; knowledge and skill with spells and how skilled mages are at tapping powerstones for power.  Davis will have limited magery in some ways, being a light mage, but will be exceptionally skilled at tapping powerstones, allowing him to accomplish tremendous levels of power in his light spells.  His wealth allows him to own more and higher quality stones than others, adding to his abilities.

The stones can also be used by non-magicians.  Most notably warriors.  Special warriors (they need a name), can be used to go beyond normal human limits.  This includes endurance, strenght, speed and recovery from injury.  This is a special ability, and these are the elite warriors in all the armies.  The exact use each warrior can make of the stones varies on their physical abilities and skills, their abilitiy to tap the stones, and the quality of stone they have (this is true of all stone users).

The other major use of stones is by crafts people.  This exists in all cultures, but is most common in Dwarvish and Goblin culure.  Compared to magic and warfare, using powerstones for craftmanship is much more subtle and focused, but follows similar general parmeters.  There will be a running theme that while fighting and magic is the most celebrated use of the stones, their real power and meaning comes from their quieter, more subtle uses, like craftmanship and other tasks.

The univerals use of stones across the continent is both a unifying and divisive cultural standard.  It is divisive because each culture values from them in different ways, and their tolerance for each others use varies from acceptance to total disgust.  This is a perpetual area of disagreement for the cultures.

It is unifying, becaus it is quickly apparent that part of the Enemy's campaign is to destroy all of the powerstones; for unknown reasons, they consider them absolutely reprehensible and sacriligous, and are willing to go to great lengths to destroy them.

Neither culture will understandwhy this is, accept that they are well established cultural norms.  The deeper reason is the galactic conflict.  The mysterious alien race has set up the planet as a test of two principles; diversity vs. sameness.  The continent represents diversity, with differences that, when working together, allow them to tap the powerstones for tremendous abilities.  The enemy represents samesness, uniformity, and their power comes from their ability to work totally in unison, always in perfect coordination, with easily replaced drones.  So the Enemy is driven to conquer and create sameness, and the continent to build a functional society out of their diversity.  The stones, and the battle to destroy or use them, is the concrete expression of that conflict.

Thus, the stones are an everpresent but subtle connection to a grand universal magical scheme.  So while the major focus will be on thenuts and bolts of creating DH, there is a universal magic and greater quest in the background.

This also links to other adventures.  Powerstones exist on multiple planets, all of them are linked, and absorb the essence of everyone who uses them.  So using the powerstones you can travel to other planets, or have realms where multiple worlds/realities overlap.  At the same time, they can used for reincarnation.  The stones absorb the essence of anyone who uses them, and under special circumstances, people are totally absorbed, and can be reincarnated.  This will happen to Davis and other key players in the second round of books.

The stones are also a way for the aliens to periodically interact and step into the world, using the stones to make contact with Davis and DH (in very rare circumstances). 

The mysterious heart of DH castle is a tremendously powerful powerstone.
Role:  universal plot device