Zincblende structure

• SiC cubic moissanite - Note: natural moissanite is neither cubic nor hexagonal. It's a more complex stacks of A,B,C layers.

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• C diamond
• Si, pure silicon
• Ge, pure germanium (rare)
• grey tin (odd)

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• ZnSe Zinc_selenide stilleite - 5.42g/ccm - Mohs 5 - (Se is rare)
• α-ZnS zinc sphalerite - 4.2g/ccm . Mohs 3.5 to 4 (soft)
• CdS cadmium_sulfide

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• are there other examples also forming pseudo phase diagram islands?

Pseudo phase diagrams surrounding SiC

All the carbon group elmenets can be substitutes.
The heavier ones likely only within bounds.
Like e.g. Lead carbide (combining the biggest and smallest atoms of the group) is not achievable via thermodynamic means.
And it's unclear if even via mechanosynthetic means.

Pseudo phase diagrams surrounding ZnS

Investigating the pseudo phase diagrams that emanate from ZnS

Replacing sulfur:

• Replacing all sulfur with oxygen (above S) likely not work since ZnO (zncite) is hexagonal.
  
• Replacing all sulfur with selenium (below S) works. thhis gives ZnSe Zinc_selenide (mineral stilleite)

Replacing Zinc:
Below Zinc there is cadmium and mercury both rare and toxic.

• CdS cadmium_sulfide has zinkblende structure => all psuedo polymorphs possible
• α-HgS cinnabarite wants to be trigonal rather than cubic - cinnabar structure

Rift between pseudo phase diagrams

SiC and ZnS have the same structure but there seems to be an unbridgable rift for pseudo phase diagrams.
With other nonmetals sulfur usually assumes bond order two (like oxygen above) but in ZnS it assumes bond order four.

Cross combining the elements leads to some odd compounds instead of a preserved structure. See:

• CS₂ is an (odd) liquid.
• SiS₂ is an (odd) polymeric compound.
• Zinc carbide ??? barely any info
• Zinc silicide ??? barely any info

Misc

• Also a very simple but different (odd) cubic structure: Cu₂O cuprite.
• Silver Ag (below Cu) does the same - Ag₂O silver_oxide (no mineral it seems)

Nonmetallicness despite high metal content:

Covalent behavior and nonmetallic optical and electrical behavious may have to do with
noble metals on the right having almost full electron shells and all electrons being used for covalent bonds no electrons left for semi-conductive or conductive behavior.
All that despite these compounds are 2/3 metal 1/3 oxygen.

• ZnO₂ ?? ...

• Complement to that ...

Related

• Simple crystal structures of especial interest
• Wurtzite structure - layers ABAB
• Zincblende structure - layers ABCABC