Okay, it's not really magic. It's physics. But it got you here didn't it?
Gemstones may not produce magic, but great gemstones seem to have a virtual magic that can mesmerize and tantalize. Here are some of the factors that make the "magic".
Some gemstones have an ability to emit visible light in darkness when exposed to ultraviolet light and we call that fluorescence.
Other gems such as Kunzite can produce an "afterglow" which lingers after light has been removed ... and we call that "phosphorescence".
Luster in Gemstones
Luster is a result of light reflecting from a gemstone's surfaces ... internal and external.
Smoother and more highly polished surfaces will show more luster. Other factors influencing luster are a gem's refractivity. The best luster will be seen in highly refractive gems such as diamond, zircon, and rutile. We call it an adamantine luster
Refraction in Gem Materials
Refraction is the bending or redirection of light as a result of entering or leaving a gemstone. We normally associate this with a gem/air interface.
Note: A gems ability to return light to the eye is compromised if the gem/air interface is compromised ... which is why dirty gems appear dull.
Be aware that some gems are singly refractive and other are doubly refractive. Double refraction is what causes the attractive color complexity of gems such as ruby and sapphire.
Dispersion in Gemstones
Dispersion is the separation of light into spectral colors ... or the rainbow effect.
Generally, highly refractive gems tend to have high dispersion. Diamond and zircon are good examples.
Pleochroism in Gem Minerals
Pleochroism creates evident color changes when gemstones are viewed from different angles. An improperly cut stone will show the poorer rather than the richer hue.