Cleavage planes
Q: Doesn't the presence of cleavage planes mean products out of nanoscale gemstones break easily?
A: No, not really.
Brittleness of macroscale gemstones is mainly a result of the unavoidable presence of defects (internal and on surface)
and continuous covalent connectivity leading to stress concentrations inducing fractures that unboundedly propagate
to a full break long (easily >99%) before the theoretical limit is reached.
Thereby massively reducing toughness.
Interlocking nanoscale gemstones like in gemstone based metamaterials
(will) remove that massive reduction. Even if the many of the cleavage planes are aligned.
★ by stopping fractures at the next very nearby non-bonded interface interlock and
★ by most crystolecules having no internal or external defects
… particularly no stress concentrating surface divest to get a cleavage plane started.
Cleaving planes as only a concern for the very highest performance applications
Cleavage planes in gemstones like diamond and are still well above 50% of the maximum ultimate tensile strength
which is still enormous and sufficient for almost all except the most extreme applications.
Plus there are a number more and less straightforward ways to improve on that
in the rare cases it is really needed. E.g.:
Approaches to mitigate for cleavage planes
Interlocking nano-gemstone crystolecules in different crystal orientations:
(very much like FFF/FDM 3D printed parts ofteh have a weaker inter layer direction adn wood has a grain.
Varying stacking order:
ABCABC is cubic ABAB is less isotropic hexagonal with a only one major axis insterad of four.
Other stacking patterns are possible too (this happens naturally in moissanite (SiC))
but one would likely want to make it in some less or more preiodic systematic pattern.
See: Checkerboard compound
Quasiamorphous and quasicrystalling structures:
Fancy stuff to look at eventually.
Obviously avoid ges with greally pronounced cleabvage planes.
Some 2D materials like e.g. slingle crystalline graphite (aka HOPG)
have just mere vdW bonds in one direction.
These are still not weak from a breaking marcoscale parts by human hands perspective
but ~100x weaker than covalent.