The term crystals in Riariti actually refer to three specific gemstones, none of which are the quartz associated with being crystal on Earth. Crystals occur rather commonly all over the world, though there are certain areas where they occur in greater numbers or in larger formations.
Rana is known on Earth as the gemstone Jeremejevite and can be colored clear, white, yellow, greenish, blue, or violet. Rana occur in well-formed, sharply crystallized, prismatic obelisk prisms with lustrous surfaces, sometimes two toned with a blue base and white terminations.
Sagara is known on Earth as the gemstone Grandidierite and can be colorless, green, or blue. Sagara forms rare prisms or grains and is found enclosed in sillimanite or between sillimanite and other minerals.
Raduha is known on Earth as the gemstone Black Opal and displays typical iridescence (up to all colors) on a black base. Raduha veins occur in the fissures of almost any kind of rock, being most commonly found with limonite, sandstone, rhyolite, marl, and basalt.
Crystals can be used in a variety of ways and so can be commonly purchased in nearly every town throughout the world. The price varies depending on the type of crystal, the location of the town in regards to any crystal mines, and the purity and condition of the stone itself. Flawed and small crystals are highly inexpensive due to being less efficient than their brethren. Larger crystals, or ones with very little to no flaws, are more expensive but last longer and are much more efficient.
When a crystal can no longer be of use, it shatters into dust. This can happen if it's used too often, it's used up completely by a spell, or filled past its capacity. In the former cases the crystal will begin to lose its lustre end become riddled with cracks until it finally shatter, and in the latter case the crystal will grow warm and emit a high-pitched noise as a warning.
Crystals can be used in their raw form, but become easier to use when they are cut and shaped.
Anchoring a spell is when someone casts a spell on an item that is intended to be activated later, either triggered by something such as a specific voice command or on a timer. Not all spells can be anchored, and the spell needs a source of mana if it's expected to be continuous. Best used in conjunction with mana-storing crystals.
Crystals can be used like a mini reservoir to store mana. It takes practice and knowledge to be able to manipulate mana itself without using it in the form of a spell, but once the method is learned storing mana becomes quite easy and very useful. Crystals with mana stored in them can be used to fuel spells without depleting one's own.
Crystals naturally draw mana towards them and work like lenses to refine it. Thanks to this, having crystals around helps spellcasters focus their magic just by default. When added to other items, like a sword or a staff, they allow a caster to more easily channel a spell through them to augment the equipment with less mana loss, requiring less concentration.