If you broke open the diamond, the sample would be destroyed. They used a technique called x-ray crystallography. You shoot a beam of x-rays at the sample, and

If you broke open the diamond, the sample would be destroyed. They used a technique called x-ray crystallography. You shoot a beam of x-rays at the sample, and the beam deffracts due to the crystal's atomic structure. In analyzing the resulting diffraction pattern you can build a *3D model of what the molecules look like structurally. This is why we know what DNA looks like. https://en.m.wikipedia.org/wiki/X-ray_crystallography https://en.m.wikipedia.org/wiki/X-ray_crystallography