Synthetic diamond "nanocrystalline" and "microcrystalline" diamond, respectively. Synthetic diamond is the hardest known material, where hardness is defined as resistance to indentation. The hardness of synthetic diamond depends on its purity, crystalline perfection and orientation: hardness is higher for flawless, pure crystals oriented to the <nowiki>[</nowiki>111<nowiki>]</nowiki> direction (along the longest diagonal of the cubic diamond lattice). Nanocrystalline diamond produced through CVD diamond growth can have a hardness ranging from 30% to 75% of that of single crystal diamond, and the hardness can be controlled for specific applications. Some synthetic single-crystal diamonds and HPHT nanocrystalline diamonds (see hyperdiamond) are harder than any known
Anisodesmic crystal anion equals the charge on that anion." When there is more than one type of bonding in a crystal, strongly anisotropic physical properties can result such as those of graphite. Many other substances have anisotropic physical properties. Such properties are directly related to the atomic structures of the substances. Conversely, halite is an example of an isotropic crystal with equal hardness in all directions. Anisodesmic crystal An anisodesmic crystal (sometimes anisodemic crystal) is a crystal containing bonds with differing electrostatic valencies. All other crystals are known as isodesmic crystals (or isodemic) and examples include diamond and halite. These terms are