They appear as minerals, despite their airy nature. For example, true air is weightless but has form. In fact, using True Air as an element in a weapon makes it lighter than it was before. True Air can only be found in the upper atmosphere, near mountaintops as it grows inside of clouds. The Theran Empire of Earthdawn millieu used huge airships powered by blood magic to scour the clouds for true elements which they used in their wards before the Scourge occurred.
True Air appears as a silvery transparent crystalline metal. It is basically weightless, and will reduce the weight of an object that contains it and improves it's flight properties. Missile weapons will gain a greater range, et al.
True Earth a coppery half-metallic, half-earthen material. True Earth is not very heavy but is very tough, tougher than most modern alloys.
True Fire appears as a fiery golden crystalline metal. True Fire generates constant heat, and if made into foci, that heat can be channeled and controlled.
True Water is a mercurial semi-solid crystalline metal. True water will "sweat" small amounts of water, additionally, it will purify water that is is submerged in.
True Wood grows from trees that are fertilized and grown with true elements in the soil. The Joshua Tree Monument might be an example of True Wood.
Each True Element has special properties and are highly "aspected" toward their respective element. For example, making a Spirit Focus with True Earth will be naturally good regardless of the type used, but it will be much better when used to make a Focus to summon Spirits of the Land, Gnomes, and Earth Elementals. Additionally, weapon foci made with True Elements assume the basic primary and secondary elemental effects of their chosen element. As such, a True Fire sword will start things on fire, harm water spirits, and constantly generate steam when submerged in water.
As for during enchanting, treat the True Elements as radicals, double the bonuses available if the focus is aspected towards the element. True Wood is aspected towards Health Spells. Weapon Foci gain the the basic bonus but also receive the additional elemental effects.
I speculate that there are other True (elements) such as True Light, True Ice, and True Lightning, but these are just vague guesses.
