Base materials with high potential

Best of the best

• diamond and its polymorphs including hexagonal diamond aka lonsdaleite

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• moissanite - SiC - high heat resistance
• stishovite and seifertite - metastable ultrahard and dense SiO₂ polymorphs

Simple rutile structure & hard

• rutile TiO₂
• stishovite - metastable SiO₂ polymorph - rutile structure & very hard and dense
• Neo-polymorphs of the above

Simple salt structures

• Periclase
• Some transition metal monoxides

Con: low crystal structure symmetry

• leukosapphire - very hard
• quartz

Con: Rather soft materials

• Calcite and aragonite