Initially, I envisioned the crystals in a permanent fixture, like the wall of a cave. Three rows of three crystals, each row a different shape. Three-sided crystals, four-sided crystals, and six-sided crystals. Since the permutations were limited to six arrangements, there were 216 possible combinations. Kleenex tissues came out at one time in pretty holographic type boxes. I cut them up and made my own crystal wall!
The wall and crystals have changed a bit over the years, as you can see in this before and after image:
The caves were used for over a thousand years before a more portable device was created. Neala's box was one of these. The additional crystals on the box was merely to draw attention away from the nine moveable ones.
So I made a box!
I'm not great with wood carving, unless it's a stick for a hot dog! So I had to get creative.
The crystals themselves are not necessarily of Earthly origins.
It is noteworthy to mention here that this box itself is over 200 years old. Modern portals are operated using a small handheld device which contains, in its sealed interior, crystals which would be connected digitally, removing the likelihood of losing a crystal and being marooned.