Ternary and higher gem-like compounds

Look out for rock forming minerals here.
Note that with mechanosynthesis it is possible to control of solid solutions series. By "normal" thermodynamic means (that is melting and recrystallisation) atoms that are chemically similar can randomly swap places. Mechanosynthesis (which does not involve heating the material) can place those atoms in non random checkerboard-patterns where they stay if the material is kept cold (here cold can mean room temperature and more). See "pseudo phase diagrams" and "neo-polymorphs" for more information.

most common metal rich core mantle transition zone minerals

In the earths mantle and crust silicon and oxygen are the most abundant elements. On the borther to earths outer core this changes to iron and nickle. Down there the most abundant minearls are made from mixture of those elements. As a sidenote: In nature when iron rich metal is available in stochiometric excess heterogenous pallasite is formed. This rock looks really beautiful and can be found in some meteroids - recommendation to check it out.

• mixing series of olivine (wikipedia) / peridot (wikipedia) - (Mg,Fe)2SiO4
• with high pressure modifications: wadseylite (wikipedia) and ringwoodite (wikipedia)

Of interest as diamondoid materials may be the pure end members of the mixing series:

• Fayalite Fe₂SiO₄
• Forsterite Mg₂SiO₄
• Tephroite Mn₂SiO₄ (less interesting since Mn is more scarce)
• Titanium Silicate TiSiO₄

related minerals:

• Ca(Mg,Fe)SiO₄ - wikipedia: magnesium and iron monticellite
• CaTiSiO₅ - wikipedia: Titanite or Sphene (optical dispersion exceeding diamond; birefringent)
• Mn₃Al₂(SiO₄)₃ - wikipedia: spessartine - (with rather rare Manganese)
• FeTiO₃ - wikipedia: Ilmenite
• Al₂SiO₅ andalusite Wikipedia:Andalusite Mohs 6.5-7.5 and kyanite Wikipedia:Kyanite Mohs 4.5-5 & 6.5-7

The spinell group (wikipedia)

These oxide minerals are devoid of the ubiquitously present silicon.

aluminum spinells

• MgAl₂O₄ - wikipedia: spinell
• FeAl₂O₄ - wikipedia: hercynite
• (Mg,Fe)Al₂O₄ - wikipedia: caylonite - mixing series inbetween the former two
• ZnAl₂O₄ - wikipedia: gahnite
• BeAl₂O₄ - wikipedia: crysoberyll
• MnAl₂O₄ - wikipedia: galaxite - (with rather rare manganese) - image

iron spinells

• MgFe₂O₄ - wikipedia: magnesioferrite
• TiFe₂O₄ - wikipedia: ulvöspinel
• ZnFe₂O₄ - wikipedia: franklinite
• NiFe₂O₄ - wikipedia: trevorite
• MnFe₂O₄ - wikipedia: jacobsite - (with rather rare manganese)

related compound:

• ZnFe₃O₄ - wikipedia: zinc ferrite - synthetic zinc ferrites

Alkali and earth alkali compounds

They tend to be rather soluble in binary compounds (you won't find many there) in ternary and higher compounds they tend to form less water soluble minerals. See: compounds with s-block metals

• Ca(OH)₂ calcium hydroxide aka slaked lime (rather water soluble)
• CaCO₃ calcium carbonate (very slightly soluble)
• MgCO₃ magnesium carbonate aka magnesite (slightly soluble)
• Mg₃B₇O₁₃Cl boracite (very slightly water soluble)

Other

• Various silicates [1]

Another interesting tertiary material falling in this scheme would be CSiO ₄
a solid intermediate material between CO₂(gas) SiO₂(solid quartz): [2] (A prototypical pseudo phase diagram.)

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• AlPO₄ berlinite Wikipedia:Berlinite Mohs 6.5 (similar to quartz)
• MnCO₃ rhodochrosite [3] Mohs 3.5-4
• MnSiO₃ rhodonite [4] Mohs 5.5-6.5
• Na4Al3Si9O24Cl marialite Mohs 5.5-6 (scapolite end member)
• Ca4Al6Si6O24CO3 meionite Mohs 5-6 (scapolite end member)
• Cu₂FeSnS₄ stannite [5] (contains unabundant copper and tin) Mohs 4