Base materials with high potential

Very good materials

Best of the best

Best diamondoids

• C – diamond and its polymorphs including hexagonal diamond aka lonsdaleite
• SiC – moissanite – high heat resistance
• Si – pure silicon (eventually)
• BN – boron nitride (cubic c-BN and hexagonal w-BN) – (boron is not super extremely abundant and available)
  BN – quingsongit (de) – cubic – Mohs 9-10
• AlN – aluminum nitride – (less strong and less chemically stable than boron nitride but aluminum is boundlessly available)
• BC₂N – heterodiamond

Related: Diamond like compounds

Not diamond structure:

• B₄C – boron carbide – same abundance issue as above plus more complex unit cell

Best SiO₂ polymorphs

Metastable ultrahard and dense SiO₂ polymorphs:

• SiO₂ stishovite (tetragonal rutile structure)
• SiO₂ seifertite (orthorhombic scrutinyite structure)

Simple titanium gemstones

Titanium combined with all sorts of abundant non-metal elements forms astoundingly many gemstone like compounds with exceptionally good mechanical and thermal properties. (Unlike the extremely abundant element iron that disappointingly underperforms in this regard). Titanium is reasonably abundant in Earths crust. Not as common as iron though. Titanium is especially common on our moon. There is also lack of non-volatile non-metal elements (like carbon and nitrogen) to combine it with though. Well, even for a quite big moonbases the volatiles in polar moon craters will suffice.

Titanium compounds with second row elements

• TiB₂ Titanium diboride - hexagonal 2D layered - 3230°C - 4.52g/ccm - optically metallic - highly refractory compound
• TiC Titanium carbide - simple cubic - 3160°C (800°C in air) - 4.93g/ccm Mohs 9 to 9.5 - water insoluble (almost)
• TiN Titanium nitride - simple cubic - 2,947°C - 5.21 g/cm3 - optically metallic (golden) - "barrier metal" - water insoluble (almost)

Titanium oxides:

• TiO [1] - hongquiite - simple cubic - 1,750C° - 4.95g/ccm - optically metallic (golden)
• Ti₂O₃ [2] - tistarite - hexagonal corundum structure (like sapphire) - 2,130°C (decomposes) - 4.49g/ccm - semiconducting to metallic at 200°C
• TiO₂ [3] - rutile, anatase, brookite, and more

Titanium compounds with third row elements:

• TiP - phosphid Titan(III) phosphide (de.zxc.wiki) - hexagonal - 1860°C - 3.94g/ccm - optically metallic
• Ti₃P (materialsproject.org) - tetragonal - 4.7g/ccm

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• TiSi₂ Titanium disilicide - orthorhombic (complex unit cell) - 1,470°C - 4.02g/ccm - water insoluble - optically metallic and electrically conductive - More titanium silicides ...
• Ti₃Si - tetragonal - (isotype to Ti₃P - see above and Zr₃P)
• Ti₅Si₄ - 2120°C - tetragonal (isotype to Zr₅Si₄)
• TiSi Titaniummonosilicide - 1760 °C - orthorhombic (isotype to FeB)
• Ti₅Si₉ - spacegroup Cmcm (Nr. 63) - 3.9g/ccm
• Ti₅Si₃

Given silicon is a semi-metal and titanium is a metal titanium silicides should come with quite metallic properties (optically and electrically).
But mechanically still gemstone like like inter-metallic compounds.

Simple zirconium gemstones

Zirconium Zr compounds (maybe)

• Zr (fifth row) is the element below Titanium (fourth row)
• Zr is the most abundant fifth and below row non alkali element (Earth's crust).
• Zr makes similarly good compounds with various other elements as Ti

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• Wikipedia: Zirconium: oxides, nitrides, and carbides
• ZrC zirconium carbide very high melting point (~3530 °C)
• ZrN zirconium_nitride –
• ZrP ??
• ZrO
• ZrO₂ Baddeleyite (aka cubic zirconia)
• ZrSiO₄ Zircon (zirconium silicate)

Quite simple rutile structure & Hard

• Rutile TiO₂ – Mohs 6.0 to 6.5
• Stishovite - metastable SiO₂ polymorph - rutile structure & very hard and dense – Mohs 8.5 to 9.5

And neo-polymorphs with rutile structure. These include:

• Silicon group: GeO₂, SnO₂, β-PbO₂ – (germanium Ge is rather rare)
• Other: MnO₂, FeSbO₄ – (antimony Sb is rather rare)

See: rutile structure. There is also a mention on that on the page about silicon
This could be called the the stishovite continuum or the rutile continuum'.

Corundum structure & hard

The corundum structure has lower symmetry than the rutile structure
which can be but not necessarily is a downside in that the design of crystolecules
based on these materials might be more difficult and or more limited.

• Leukosapphire (Al₂O₃) – Mohs 9 (defining mineral)
• Tistarite (Ti₂O₃) – Mohs 8.5 – optically metallic

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• Eskolatite (Cr₂O₃) – Mohs 8 – optically metallic – Chromium is less common
• Hematite (Fe₂O₃) – Mohs 5.5 to 6.5 – optically metallic – Iron compounds are usually weaker

For more examples including less performant ones see:
Corundum structure – corundum is a term for low grade sapphire (and polymorphs: deltalumite)

Mono metal monoxides (simple cublic NaCl salt structure)

Earth alkali based

• MgO periclase
• CaO anhydrous lime - questionable - highly reactive with water - ok if well sealed inside of products

Transition metal based

Some transition metal monoxides (Typical: Max 1300-1900°C - Mohs 5-6)

• TiO hongquiite
• MnO manganosite - (Mn is less abundant)
• FeO wüstite
• NiO bunsenite - (Ni is not too abundant on earth but very abundant on metallic asteroids)

V vanadium, Cr chromium, Co cobalt do that too but
these elements are more scarce thus
not included as pure high volume base materials here

Other quite interesting compounds

Decently hard iron nitrides:

• Fe₄N Roaldite 3D structure (de) – cubic – Mohs 5.5-6.0 – (very simple crystal structure)
• Fe₉N₄ Siderazot 3D structure (de) – triclinic – Mohs ?? – (not as complex as formula suggests)

Silicon oxynitride:

• Si₂N₂O Sinoite [4] silicon oxynitride [5] 3D structure (de) – ortorhombic pyramidal – 2.83g/ccm

Corundum/sapphire polymorphs (See: Leukosapphire#Polymorphs):

• Al₂O₃ Deltalumite (δ form of corundum, polymorph of sapphire) – tetragonal – Mohs ?? (likely quite hard) – [6]

Spinel minerals (they all have nice cubic unit cells)

• Spinel MgAl₂O₄ – Mohs 7.5 to 8.0 – cubic
• Ulvöspinel TiFe₂O₄ – Mohs 5.5 to 6.0 – optically metallic

Ambient pressure stable high pressure modificaions of olivine:

• High pressure modification of iron olivine γ-Fe₂SiO₄: Ahrensite – [7] – (Mohs 6 – 4.26g/ccm)
• High pressure modification of magnesium olivine Mg₂SiO₄: Ringwoodite – (Mohs ? – 3.9g/ccm)

Quite good materials with some hampering weakness(es)

Con: low crystal structure symmetry

• Al₂O₃ – leukosapphire - Mohs 9 (defining material) - (isostructural to Ti₂O₃ tistarite?)
• β-C₃N₄ – beta carbon nitride – (possibly a fire hazard)
• Si₃N₄ – silicon nitride
• Si₃N₄ – nierite 3D structure (de) – Mohs 9
• SiO₂ – common quartz - and other low density polymorphs of SiO₂

Con: Somewhat soft materials

Saving graces: very common or acessible elements, some degradability, nature friendliness (common biomineral – sea shells)

• CaCO₃ calcite – trigonal – Mohs 3 (defining mineral)
• CaCO₃ aragonite – ortorhombic – Mohs 3.5-4.0 – (a bit harder and somewhat higher symmetry crystal structure)

Others

• BeO brommelite [8] – excellent material – hexagonal – simple minimal unit cell (de) – very hard Mohs 9

Problems:

• beryllium is quite scarce
• beryllium is quite poisonous – it's can be quite well sealed in a macroscopic gemstone though – brommelite gemstone based nanomachinery: not so clear

Garnets

X₃Y₂(SiO₄)₃ the class of garnet gemstones [9] – typically hard Mohs 6.6-7.5 – and cubic – but big unit cell

• Andradite – Ca₃Fe₂Si₃O₁₂ – iron but no aluminum garnet – HUGE unit cell 3D structure (de)

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• Almandine – Fe₃Al₂Si₃O₁₂ – iron and aluminum garnet
• Pyrope – Mg₃Al₂Si₃O₁₂ – aluminum but no iron
• Grossular – Ca₃Al₂Si₃O₁₂ – aluminum but no iron

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• Spessartine – Mn₃Al₂Si₃O₁₂ – (less abundant manganese)
• Uvarovite – Ca₃Cr₂Si₃O₁₂ – (less abundant chromium – neither aluminum nor iron)

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Wikipedia:

• Category:Garnet_group
• Category:Garnet_gemstones

Related

• Gemstone like compound and Diamond like compounds
• Simple crystal structures of especial interest
• Can we make these high potential base materials from random stones lying around on the ground?
  Yes! See: Common stones
• Abundant element
• High performance of gem-gum technology

External links

Wkipedia:

• Category:Superhard_materials (Note: Many of them incorporate very rare elements)
• Superhard material