Here it is.

I like simple, geometrical forms and I like Lego. So I built an octahedron with Lego bricks. Because it looks like a gemstone and because some of its bricks are super rare (just like gems), I called it the Lego octahedron gemstone. Here it is:

It is size 6 (6 rows of slope bricks and 6 rows of inverted slope bricks) and has the color dark stone grey (color ID: 199).