White sapphire

Terminology

"White sapphire" (meaning clear transparent colorless) because we want to focus on perfect crystals without any color giving impurities.
A base material for gemstone metamaterial technology would be perfectly impurity free and colorless clear.

Just "sapphire" usually refers to sapphires with impurities (iron and titanium ions replace aluminum ions) causing a blue to black color.
Also called lecosapphire or leukosapphire (may be more prevalent in German).

Advantages of this gem

• very hard material (Mohs 9 – defining mineral), very high heat conductivity
• made out of the extremely common element aluminum (more common than carbon in diamond or moissanite)
  Possibly helpful on the Moon with carbon being scarce.
• like moissanite sapphire is thermodynamically stable not just metastable like diamond thus very heat resistant
• Crystal structure: trigonal – Not as high symmetry as cubic but still good.

Maybe look at metastable Al₂O₃ polymorphs at the eventual cost of somewhat less heat resistance?

Related

• Deltalumite – a tetragonal polymorph of Al2O3 with spinel structure
• Tistarite Ti₂O₃ has the same structure. => neo-polymorph series?
• Gemstone like compounds with high potential – Gemstone like compounds
• Corundum structure – Simple crystal structures of especial interest
• Aluminum oxides
• Moissanite is also an extremely heat resistant base material.
• Diamond is much less heat and oxidation resistant.
• Both diamond and moissanite have higher crystal structure symmetry than leukosapphire

---

• Base materials with high potential

Polymorphs

Deltalumite Al₂O₃ (δ form of corundum, polymorph of sapphire) – tetragonal – Mohs ? –

Trivia

• 🟥 (Red) ruby is just red sapphire. Color from Chromium Cr.
• 🟦 Classic blue is from elements (Fe,Ti)
• ⬜️ transparent, no impurities, white sapphire
• 🟨 There are many other possible colors from impurities/dopants.

---

• 🟢 (Green) emerald is NOT a form of sapphire but a form of Beryl
  a beryllium aluminum silicate harder than typical silicates.
  Beryllium is a quite rare element so forms of beryl are not that viable as a structural material.

External links

Wikipedia

• Corundum
• Sapphire
• Ruby

---

• materialsproject.org [1]
• mineralienatlas (de) [2]
• Strukturtypendatenbank uni-freiburg: [3]
• Wikidata leukosapphire: https://www.wikidata.org/wiki/Q3831236