Charts for gemstone-like compounds

This page is a collection of the gemstone like compounds that seem the most useful/promising/interesting/awesome/... for the use in products of advanced gemstone metamaterial products. Diamond will not be included here, Historically a (motivated) strong fixation on diamond has been drawing attention away from the so many other interesting potential building materials.

Note that this chart contains opinion of the author (APM:About). The readers favorites may differ.

Mosissanite SiC (cubic & hexagonal !!)

This is essentially diamond and lonsdaleite (hexagonal diamond) with every second carbon atom replaced with a silicon atom.

• Unlike silicon it's transparent in the visible spectrum and.
• It has much better thermal resilience than diamond (it's stable not meta-stable - there's no desire to turn to graphite at high temperatures)
• Macroscopic amounts (not finely dispersed) are self fire extinguishing. An oxygen excluding liquid glass slack layer prevents sustainment of fire.
• At places in the solar system where carbon is scarece (moon presumably) it doubles the building material.

Common knowledge: It's almost as strong as diamond (theoretical limit). It has a higher refractory index than diamond (and has double refraction)

Note that today's (2017) moissanite specimens, which are produced by thermodynamically means, have neither cubic ABCABC nor hexagonal ABAB stacking order. Depending on the production method different more complex patterns emerge.

Stishovite SiO₂ (& Rutile TiO₂ & ...)

This is essentially quartz with a better crystal structure.

• It consists out of the two most common elements on earth silicon and oxygen.
• In contrast to quartz it has a much higher hardness (Mohs 9)
• In contrast to christobalite (another very hard polymorph of quartz) it has a crsytal structure with higher symmetry (tetragonal)
• The crystal structure (Rutile structural type) matches many other interesting compound allowing transitions. See: "Pseudo phase diagram"

The issue: Just like diamond it's only metastable, so probably not suitable for very high temperature applications.

Cubic gauche carbon nitride

• Just like diamond this stuff can be made out of air. On earth nitrogen is much easier to filter out of the atmosphere than carbon dioxide. Thus one can produce faster when the air stream is the limiting factor. Side-note: this does not apply to Venus "air" and Titan "air" since there carbon is as abundant as nitrogen. In Mars' thin atmosphere the situation is reversed. There nitrogen is scarce relative to carbon dioxide.
• In contrast to beta carbon nitride its crystal structure has higher symmetry (cubic aka isometric).
• very strong but metallic conductivity (exotic property)

There's a tiny issue though: It may be a fire hazard or even explosive. (silicon nitride is not)

External Links:

• Synthesis of Ultra-incompressible sp³-Hybridized Carbon Nitride with 1:1 Stoichiometry
• Single-bonded cubic form of nitrogen

Non-sapphire polymorphs of aluminium dioxide

Sapphire crystal structure has an inconveniently low symmetry. There are other polymorphs without that problem. They are just metastable though.

Degradable / Biominarals

Periclase (MgO)

Magnesium is one of the most common elements (lots of it can be found in seawater)

• It is just so very slightly water soluble. This makes it nicely "bio-degradable" since there is no fast massive magnesium salt release.
• It has (as most simple salts) a high symmetry cubic crystal structure.

The issue: the ionic salt like character may prevent one from using it for sliding nanoscale interfaces and deem it to just structural uses.

Further

Water insoluble calcium salts: (Wikipedia: [1])

• phosphate => appatite (hexagonal and decently hard - Mohs 5)
• carbonate => aragonite (higher symmetry than calcite - orthorhombic - and a bit harder - Mohs 4)
• titanate => perscovite (decently hard - Mohs 5 - but only mid level symmetry: orthorhombic)

Water insoluble magnesium salts:

• carbobnate => magnesite (decent symmetry - trigonal)

• Dropouts: silicate => wollastonite (drop out since too low symmetry - triclinic); sulfate => gypsum (drop out since way too soft - Mohs 2); nitrate => no mineral? (drop out too since highly water soluble)

Iron compounds:

• pyrite (high symmetry cubic - probably one of the easiest entry points for gemstone mechanosynthesis)
• wüstite (iron monoxide) - cubic salt like structure (advantage: many other transition elements form the same structure and can be substituted!);
  Hematite (decent symmetry - trigonal); Magnetite (high symmetry - cubic - but big unit cell)
• iron titanate => illmenite (decent symmetry - trigonal)