Base materials with high potential

Very good materials

Best of the best

Best diamondoids

• diamond and its polymorphs including hexagonal diamond aka lonsdaleite
• moissanite - SiC - high heat resistance
• pure silicon (eventually)

Best SiO₂ polymorphs

Metastable ultrahard and dense SiO₂ polymorphs:

• stishovite (tetragonal rutile structure)
• seifertite (orthorhombic scrutinyite structure)

Simple titanium gemstones

• TiN, TiP, TiC, TiSi₂, TiB₂, TiO₂, Ti₂O₃

Quite simple rutile structure & Hard

• rutile TiO₂
• stishovite - metastable SiO₂ polymorph - rutile structure & very hard and dense

Neo-polymorphs with rutile structure
See: the stishovite continuum currently on the page about silicon
Silicon group: GeO₂, SnO₂, β-PbO₂
Other: MnO₂, FeSbO₄

Mono metal monoxides (simple cublic NaCl salt structure)

Earth alkali based

• MgO periclase
• CaO - questionable - highly reactive with water

Transition metal based

Some transition metal monoxides (Typical: Max 1300-1900°C - Mohs 5-6)

• TiO hongquiite
• MnO manganosite - (Mn is less abundant)
• FeO wüstite
• NiO brommelite - (Ni is not too abundant on earth but very abundant on metallic asteroids)

V vanadium, Cr chromium, Co cobalt do that too but
these elements are more scarce thus
not included as pure high volume base materials here

Other

• spinell MgAl₂O₄ - very hard and cubic

Materials with some weakness

Con: low crystal structure symmetry

• leukosapphire - very hard
• quartz - and other low density polymorphs of SiO₂

Con: Rather soft materials

• calcite and aragonite

Others

• garnets - hard and cubic (but big unit cell)
• brommelite BeO - very hard but beryllium is scarce and poisonous