Gemstone-like compound

Diamondoid materials encompass all materials that

• do not diffuse at room temperature
• are stiff enough to keep their shape under thermal movement
• have dense three dimensional networks of covalent bonds - (short bond loops => no polymeres)
• (not necessarily but desirable) do not react or dissolve in water

If one looks at the most common / most accessible elements and their simplest compounds one finds a list of potential structural building materials:

Compounds that do not react or dissolve in water:

• carbon in diamond lonsdaleite or intermediate forms
• silicon carbide (also cubic or hexagonal)
• silicon (also cubic or hexagonal)
• B4C boron carbide
• SiB4; SiB6 ?
• four allotropes of elementar boron
• AlB12
• beta-C3N4 beta carbon nitride
• N4Si3 silicon nitride
• cubic BN cubic boron nitride
• BP boron phosphide
• SiO2 quartz (& allotropes)
• Al2O3 aluminum oxide - aka sapphire

Surisingly titanium forms chemically rather stable compounds with many nonmetals.

• TiC titanium carbide
• TiSi2 ?(unknown properties)
• TiB2 titanium diboride
• TiN titanium nitride
• TiP Titanium Phoshide (too metallic?)
• TiS titanium sulphide
• TiO2 Ti2O3 titanium oxides