Lunarite

Also called Aenilisne, 'moon-glass', this gem gives off a continuous blue glow. It is made by elven artificers by capturing the light of the moon during midnight rituals. Tel Edhil is almost exclusively lit by lunarite lamps.

If a spellcaster knows both Continual Flame and Moonbeam, they can convert 150gp of crystalline quartz into 300gp worth to lunarite by casting both those spells in an hour-long ritual at midnight during a full moon.

Lunarite is graded by how much light it gives off, and is usually referred to on a scale: new-moon, waning, crescent, waxing, full-moon. Full-moon lunarite is the brighest, and most valuable.