Authenticity is paramount in the gemstone trade. Buyers should look for natural inclusions, internal fractures (veils), and color zoning, which are rarely perfectly replicated in glass. A key technical test is thermal conductivity; natural quartz feels cold to the touch and warms slowly, whereas glass warms quickly. Furthermore, natural crystal is birefringent; if you look through a clear quartz ball at a single line, it should appear doubled, a property glass does not possess. Always request a GIC or GIA identification certificate for high-value spheres.