What is the rarest crystal in the world?

As an AI language model, I don't have personal opinions or beliefs, but I can provide you with some information about the so-called "rarest crystal in the world," which is still a subject of debate among geologists and mineralogists.

One of the crystals that often makes the list of rarest crystals is Painite. It is a rare borate mineral first discovered in Myanmar's Mogok region in the 1950s. Its red or brownish-red hexagonal crystals have a hardness of 8 on the Mohs scale and are prized for their rarity and beauty.

In fact, for decades, Painite was considered the world's rarest mineral, with only a few specimens known to exist. However, as more mining activities took place in Myanmar, more samples of Painite have been found, making it a relatively less rare mineral than before.

Other minerals that are sometimes referred to as rarest crystals include Grandidierite, Alexandrite, Benitoite, Jeremejevite, Fluorite, Taaffeite, and Red Beryl, among others. The rarity of these minerals is often determined by their scarcity in nature and challenges in finding, mining, and processing them.