Rutile

Rutile is a polymorph of titanium dioxide (TiO₂)
It may be of peculiar interest because:

• it contains the element titanium (Ti) whitch is one of the more abundant elements in earth crust.
• it has a reasonably high hardness (mohs 6.0 to 6.5)
• it features a reasonably simple (tetragonal) crystal lattice (in fact it's the defining minearal for the rutile structure)
• with the rutile structure it features the exact same structure as stishovite (a peculiarly interesting SiO₂ polymorph) but given it occurs naturally in high quantities (unlike stishovite) it likely has a higher thermodynamic stability. That is: it's less prone to diffusion into a more stable polymorph at higher temperatures.

Given both rutile and stishovite feature the same crystal structure it may be possible to mechanosynthesize checkerboard neo-polymorphic transitions by replacing some Ti with with Si in a regular pattern.

Other polymorphs of (TiO₂)

Another polymorph of (TiO₂) is anatase (mohs 5.5 to 6.0).
It also has a simple tetragonal crystal lattice but different from the rutile structure in that the unit cell is a bit bigger.

A third polymorph of (TiO₂) is brookite (mohs 5.5 to 6.0).
It also has a bigger unit cell than rutile and has the lower orthorombic crystal structure symmetry which may make it a bit less interesting as a potential base material.

Misc

• All (TiO₂) polymorphs have a high refractive index

Potential elements for controlled mechanosynthetic substitution for doping or the creation of neo-polymorphs include:

• iron Fe (extremely common) – a common natural impurity of rutile
• niobium Nb (less common) – a common natural impurity of rutile
• tantalum Ta (extremely rare) – a common natural impurity of rutile
• possibly silicon Si – since it forms an oxide with exactly the same crystal structure as rutile (stishovite)

Elements that also shares the rutile structure:

• the germanium dioxide mineral argutite (wikipedia) (germanium is one of the more rare elements though)
• the tin dioxide minearl cassiereite (wikipedia) (tin is a bit more common than germanium)
• ...

Interplanetary applications (Moon)

• Titanium is supposedly especially abundant on the moon so future gem-gum products on the moon may feature a lot of rutile for structural parts.

Related

The emenets in the Silicon group like to kake on rutile structure too.
A lot of neo-polymorphs may become possible by swapping out some of the titan for other compatible elements.

External links

• https://en.wikipedia.org/wiki/Rutile (tetragonal | mohs 5.0 to 6.5 | 4.23 g/ccm)
• https://en.wikipedia.org/wiki/Anatase (tetragonal | mohs 5.5 to 6.0 | 3.79 – 3.97 g/ccm)
• https://en.wikipedia.org/wiki/Brookite (orthorhombic | mohs 5.5 to 6.0 | 4.133 g/ccm )