What everyone Ought to Know about Gemstone Cleavage
We're not talking a walk on the beach here, but gemstones. While the word cleavage may bring to mind something other than rocks and precious gems coming out of the ground, it's a very important term in the lapidary world. The cleavage on a stone is the natural line within a stone where it will split.
You see, there are two ways a lapidary can cut a stone. Just like wood, stones have grains in their formation, and they are more likely to break along those grains if you can figure out where they are. The benefit of this kind of breaking is that by the stone continuing to separate from itself along the natural line, the lapidary knows where the cleave will be, and knows that the surface of the cleavage will be equal on both sides.
It's essentially the old 'weakest link' game. When a rock is being formed, there re always a few areas that are not quite as sturdy as the rest, this is their natural cleavage. Once a lapidary finds this cleavage, he can exploit it, easily splitting the rock along this natural line. Often this can be done as easily as putting the tip of a knife blade into the line of cleavage and tapping it what a hammer, and the crystal will separate into two pieces.
Why do they care? By finding a cleavage in a stone a lapidary can split the stone at this point, saving precious crystal material, by not having to cut it. He can then start to create gemstone shapes out of these smaller pieces. If there is no convenient cleave line, that extra crystal is just ground away, and goes to waste.
And like the other type of cleavage some stones have it (like mica) some stones don't (like aquamarine).
