I have another question about diamonds that might have a factual answer. In a diamond crystal, each of the carbon atoms it covalently bonded to four other carbon atoms in a tetrahedral shape. But what about carbon atoms on the surface of the crystal. How are the bonds of these surface atoms configured? Wouldn’t it have to be something other than a tetrahedron?
One might speculate about configurations on the corners and points of a cut diamond. I would suggest that if you “look” closely enough at these corners and points you would discover that they are actually just curved surfaces.
There’s a reason that crystals are shaped in ways that resemble their lattices or some arrangement of their lattices. It’s precisely to minimize any non-bonded atoms - in a “perfect” crystal, you’d just stack the unit shapes so that they repeat endlessly.
But in diamond, a “perfect” crystal like that isn’t possible at the surface. So what happens is that the surface structure of a diamond more closely resembles graphite.
Bond length and type - it’s what happens when you take a <111> slice through the diamond lattice, it’s like a single layer of graphite. Orientation isn’t meaningful here - the <111> diamond orientation isn’t the <100> orientation of graphite so it doesn’t translate.
Now, in most (natural) diamonds, there’s also going to be oxygen bonded at that surface. That’s what renders diamond hydrophobic.
There’s stuff you can do to diamonds to change that property, essentially doping just the surface with other substances.
“more closely resembles” is incorrect. The surface of diamond resembles the interior, with dangling bonds that can be populated by various species. The OP specifically asked about how the bonds of surface atoms are configured. They are not configured in a way that more closely resembles graphite.
Although as-grown H-terminated diamond surfaces are highly hydrophobic, they become hydrophilic after oxygen-plasma treatment. Water contact angle measurements were carried out for both as-deposited and polished diamond surfaces. These were 91.0 and 62.7°, respectively, but changed to 0.6 and 20.5° after oxygen plasma treatment for 1 minute.