Crystal Fusion

Crystal fusion has an inherent danger and unpredictability not found in the 7 main colors.
The lack of predictability is due to the variableness in how the color in question was reached. If you know what colors of the first six fused to make the crystal in question, you can predict what the crystal's powers are; if not, you may not want to poke the potentially explode-y thing.
Although, since some of these crystals have great rarities, you may be more ...motivated to test the metaphorical waters.
A scenario, for the sake of example: You find two large crystals that fused together. You can see that one was red and the other blue, but there's now a sizable chunk of blue- leaning purple crystal there. That means the fused part has both properties, but will have more water/fluid based magic than the thermal control magic. It's probably gonna be okay, knowing the way blue magic behaves. And yet... unless you already have a red magic affinity, you're gonna need a bit of strategy to make sure the red part doesn't hurt you.
Okay, so how does this apply to anything else?

Explanation

There are 7 main colors and there are 7 elemental powers. There are, then, 7 points to start from when crystals fuse. That purple crystal from earlier was 1x red and something like 2x blue. But it could have been 1x magenta and 1x blue, and thus you'd have a fusion of gravity and liquids control. Or even 2x magenta and 1x blue, which would be a fusion of gravity and solids control.
The table following serves as a way to narrow down what you might run into with crystals and mages of these colors, not as a complete statement. Fusions are not always this precise. (Like many things in the multiverse, yes?)

There is a partial understanding of 12 more colors, but they are even more rare and unpredictable than the previous 6, due to the 4:1 ratios they are.
Poking that bear is.. inadvisable, given the lack of knowledge. That's not to say that they have to be dangerous, as there are tribes (nomadic and otherwise) that have such crystals and affinities. However, even trained experts have died as a result of explorations with these colors.
I'll provide a table of these colors, but I only do so as an educational warning, not an invitation to mess with these.
(table goes here)
This RGB and hex values table is included so that a reader may look up exactly what I mean with all these color names.
(table goes here)

Type

Natural