Material properties of diamond

Hardness: Diamond is the hardest known naturally occurring material, ranking 10 on the Mohs scale of mineral hardness.
Crystal structure: Diamond has a specific type of cubic lattice called diamond cubic, with each carbon atom covalently bonded to four neighbors.
Refractive index: Diamond has a high refractive index of 2.417, giving cut diamonds their brilliance.
Solubility: Diamond is resistant to acids but dissolves irreversibly in hot steel.
Other characteristics: Diamond has a boiling point of none and a very low vapor pressure before decomposing in the solid state.

Varieties of diamond

Ballas: Spherical, radial structure, cryptocrystalline, opaque black.
Bort: Poorly formed, cryptocrystalline, shapeless, translucent.
Carbonado: Massive, microcrystalline, opaque black.
Euhedral crystals: Well-formed octahedra and twinned, flattened octahedra with a triangular outline.
Rounded diamonds: Often coated in a gum-like skin, producing a scaly or corrugated appearance.

Diamond hardness: Diamond has a hardness value of 167GPa for a surface perpendicular to the [111] crystallographic direction when scratched with a nanodiamond tip.
Crystal structure comparison: Bulk cubic boron nitride (c-BN) is nearly as hard as diamond, while beta carbon nitride (β-C) may be as hard or harder in one form.
Tensile strength: The precise tensile strength of diamond is unknown, but it can be as high as 90-225GPa depending on factors such as sample volume and lattice perfection.
Compressibility: Diamond has one of the smallest compressibilities of any material.
Cleavage and directional hardness: Diamond has a perfect and easy octahedral cleavage, with the hardest direction being the diagonal on the cube face.

Color variation: Trace impurities and structural defects in diamond are responsible for the wide range of colors seen.
Electrical and thermal properties: Most diamonds are electrical insulators and efficient thermal conductors.
Specific gravity: The specific gravity of diamond crystals has a small variation from diamond to diamond.
Anisotropy: Diamond is generally isotropic, with no or very weak birefringence.
Pleochroism: Diamond exhibits no pleochroism.

Hydrophobia: Due to its great hardness and strong molecular bonding, a drop of water placed on a diamond forms a coherent droplet instead of spreading out.
Lipophilia: Diamond's surface perfection combined with lipophilia results in a flat and sharp appearance of its facets and facet edges.
Surface properties: The hydrophobic and lipophilic nature of diamond contributes to its unique surface characteristics.
Water droplet behavior: Water droplets on diamond exhibit a cohesive behavior rather than spreading out.
Surface tension: Diamond's surface tension allows for the formation of distinct droplets.

Reference	URL
Glossary	https://harryandcojewellery.com.au/blogs/glossary/material-properties-of-diamond
Wikipedia	http://en.wikipedia.org/wiki/Material_properties_of_diamond
Wikidata	https://www.wikidata.org/wiki/Q5925925
Knowledge Graph	https://www.google.com/search?kgmid=/m/05bzcq