Spell crystals made of quartz are used by the Koriani sorceresses. Quartz crystals are piezoelectric. The physical properties of quartz extend beyond the ranges of humans' physical abilities, and can therefore concentrate, store, focus, and amplify those frequencies beyond the physical range of detection. Because it is a reactive mineral, a spell crystal can "react" to the electrical impulses from a human consciousness.
Forced mastery of a spell crystal implies a harmonic frequency out of phase with the frequency of a quartz crystal's natural resonance. A crystal consciousness that is enslaved that desires its own freedom will shatter, or depart.
The character of a crystal is influenced by its original source. Because the Compact restricts certain off-world knowledge and use of crystals mined on Athera, the Koriathain must employ crystals from their homeworld for magecraft. The most important of these stones, such as the Great Waystone and the Skyron Focus are never cleared because of the risk of losing the ancient proscribed knowledge stored within. This lends these crystals a menacing, chaotic quality.
Affecting a Spell Crystal
When clothed in silk or leather, the antistatic properties of the wrapping would suppress the electricity of the spell crystal. Conversely, the presence of copper amplifies the effect of the crystal. In one instance, Arithon is able to use his mastery over Shadow to temporarily deny access to a personal spell crystal.
A spell crystal can be expunged of a specific unwanted vibration (through selective resonance) without completely detuning it. A spell crystal can also be cleared through contact with salt water or salt. Dry salt, used long term, can damage a crystal's etheric matrix. In Fugitive Prince, "salt water and an iron bucket" are described as the ritual for grounding and clearing a spell crystal, and a Koriani sorceress is alarmed when elemental fire is added. The spell crystal faced with all three elements is shocked out of resonance and violently shatters, while all its wrought sigils vanish into the air. A more gentle saltwater cleansing would still lead to dissolution, but over time. The paired Koriani sorceress would experience headaches, weakness, and loss of reflexes, followed by death through organ failure from the backlash of stayed time.
When a ranking sorceress dies, the seals which contain any spellcraft tying them to their personal spell crystals (such as longevity bindings) are breached. The Senior Circle must ritually disperse these energies to prevent them from entropically leaking into the environment. Eight levels of cleansing are enacted before a final level that nullifies the patterned resonance of the spell crystal.
A spell crystal could never be used to imprison a free wraith -- the crystal would amplify the force of their malevolent rage. The imprisonment of "failed" Prime Matriarchs in the Great Waystone represents a different energetic connection based upon the fact that mastery of the crystal required the user to initially merge into it.