Fluorite
What is the best semi precious rock and why is it fluorite?
What, you aren't familiar with this subject and want an explanation?? Of course, I'm happy to oblige.
Fluorite is a mineral made up of calcium and fluorine, the same element that protects your teeth from cavities.
Despite this, fluorite is a bad choice of rock to put in your mouth due to its relative softness and water solubility, and resulting poisonous characteristics when exposed to a full digestive system. If this stone has any weak points, that would be it.
But its many great qualities more than make up for that minor flaw; its variety of colors for example.
Pure fluorite is clear and colorless, and even has applications for special lenses for microscopes, but most of the rocks you'll find contain impurities that result in a rainbow of potential colors.
Most specimens are green and/or purple, but blue and yellow aren't that uncommon, and red, pink, brown, black, and white are also possible.
Rainbow fluorite contains bands of multiple colors with varying levels of translucence, providing endless entertainment in the form of admiring these rocks.
The crystals generally grow as beautiful, squat squares. Sometimes people cut them into a more generic crystal point, but the squares are charming. 
But wait, that's not all this stone has to offer!
Fluorescence was named for this stone, which often glows under blacklight or sometimes even when heated, depending on what kinds of impurities it contains. That's right, the original glowing crystal is right here. Say "thank you fluorite", every single fantasy setting out there.
Speaking of fantasy, some people believe fluorite has mystical abilities to influence your energy.
Unfortunately, as we don't live in a world of swords and sorcery, these claims are almost always bullshit. However! Fluorite is one of the rare exceptions, and does indeed have the ability to vanquish negative emotions.
Anyone who takes a moment to admire their very own beautiful chunk of fluorite is bound to have fewer negative emotions than if they were devoid of a pretty crystal, that's just science. :) 
The fantasy aspects of this rock don't stop there though! If all of that wasn't cool enough for you, Fluorite also comes in a Cursed form known as fetid fluorite, a radioactive black stone containing uranium that traps poisonous pure fluorine gas.
Fluorite can be found all around the world, perhaps you can even hunt for some near you!
If not though, it's an easy and popular rock to find in rock stores, and isn't associated with slave labor like -SOME- pretty rocks out there.
If you can't collect any though, just grab one off this page to hold you over.
Here, take this, it's dangerous to go alone!
