Mechadensite
This is not an official name.
Allow me (author of this wiki) to be so vain and audacious as to name an unnatural and
not yet synthesizable gemstone with my primary internet pseudonym.
If you prefer a portmanteau name self suggesting would be:
- Ruthovite
- Stishotile
Contents
Stoichometry and examples
The mechadensite series:
- General formula: SixTiyOz
2*(x+y)=z
Examples:
- SiTiO4 (equistoicometric mechadensite)
- Si3TiO8 (silicon leaning mechadensite – presumably more hardness and less thermal stability)
End members are:
- rutile TiO2 and
- stishovite SiO2 (isostructural to rutile thus not quartz).
Other compatible elements (mainly tin)
There is also cassierite a hard stable tin oxide minearal in rutile structure (isostructural).
While cassiertite is a bit harder than rutile tin is a much less abundant element than titanium also it is notably heavier.
- Rutile: Mohs 6.0–6.5 density 4.23g/ccm
- Cassierite: Mohs 6.0-7.0 density 6.98–7.1g/ccm
General formula for tin-mechadensites: SixSnyOz where 2*(x+y)=z
Germanium Ge and lead Pb from group 14 may be suitable when added in sparingly.
And maybe even zirconium Zr and hafnium Hf (very rare element) being chemically similar to titanium Ti.
Alternate naming?
Likely propertiers
- high hardness (Mohs 6 to Mohs 9)
- electrically non conductive wide band-gap
- optically transparent in visible spectral range
- strong optical dispersion
- high heat conductance (but far from diamond)
Not a solid solution mixing series
Regarding "mixing series" note that this is meant as a piezomechanosyntesized checkerboard compound.
It is not supposed to be a thermodynamic solid solution with statistically distributed (random) placement of atoms.
Such a solid solution might not even be accessible via thermodynamic production pathways,
that is melting mixing and recrystallizing (possibly under bulk pressure).
It should be quite easy to figure out which Ti/Si ratios allow for symmetric checkerboard patterns
with extended unit cells of minimal size.
What is so special about this gemstone? …
Rutile TiO₂ is limited in hardness (Mohs 6 to 6.5) but thermally highly stable.
Stishovite SiO₂ is ultra hard (Mohs 8.5 to 9) but likely thermally less stable since
it's a metastable high pressure modification of quartz (SiO₂ too).
A "mixing series" may allow for combining the advantages of both by
tuning the Si/Ti ratio such that the material attains both high mechanical and high thermal stability.
Other neo-polymorphic checkerboard mixing series with same elements but different structure
Seifertite the second ultra-dense ultra-hard common quartz SiO2 polymorph.
is isostructural to the stable mineral Scrutinyite (Mohs ??, density 9.867g/ccm)
But there's evidence for stability of titanium and tin variants too.
Related
End-members:
Not via thermodynamic equilibriom production.
No solid solutions:
Involved elements:
Another "checkerboard-mixing-series" with a here given name:
Other potential neo-polymorph series: leukosapphire to tistarite
