This subject was brought up by Ionia Martin.
For those that haven’t reached book 2 yet . . . what are you waiting for? Seriously though, Trinity has enhancer gems that amplify her magic power. There is one in each palm and one in her forehead. She also gets a fourth in her bellybutton because she wants to defeat Nyx and ‘needs’ the boost. You quickly learn that Trinity having more than one enhancer gem makes her unique, so one can’t really use her as an example of their use. She does demonstrate their cultural importance.
Enhancer gems are typically purple, but they have been known to change color to match those of the chaos elf they have bonded with. As their name implies, they enhance the magic of a caster and are granted to an apprentice at the age of 15 if they are shown to be worthy. Those who are proven unworthy must find another trade or join as a front line caster, which has a high mortality rate. There is no specific place to put them, but they are most commonly found on the forehead and palms. These items are seen as a coming-of-age symbol and those who earn them are viewed as elite.
There is another coming-of-age symbol that is more subtle and is reserved for the highly skilled warriors of the chaos elf society. Anyone can train to be a warrior and it is considered an honor to get into the military instead of being forced to work the mines and other slave areas under Baron Kernaghan. Yet not every warrior is equal and those with superior prowess are given a tattoo. They are not always the same shape or color, but each one is made with a special paint that cannot be removed. If a scar is made over the tattoo then it will cover the injury and the tattoo will reappear on the body if the flesh or limb it’s on is lost. Like the enhancer gems, these warrior tattoos are symbols of status. In the older days of the chaos elves, they used the gems and tattoos to decide who is high-grade breeding material.