Do you think this crystal system would be effectively usable?

There's these 'sky crystals', essentially glowing meteorites, that fall from the sky commonly in this world. However, since the world is 90% sea, most of it lands in the ocean where humans can't reach it but mermaids can.

If it does land on land, the children who live there (adults live at sea) can crack it open to acquire magic gems. They come in various types: Fire ruby, frost sapphire, wind diamond, life emerald and lightning amethyst.

How I'm thinking they work is when you break or crack one, it 'releases' magic energy from the crack, producing the fire, frost, lightning, etc. As it breaks into smaller and smaller pieces, it gets harder to break down further in order to release more energy.

But do you think this method of using it is too chaotic or un-aimable to make the magic practically useful?