Simple compounds including more rare elements

Still much to add here.

Transiton metal oxides

https://en.wikipedia.org/wiki/Category:Transition_metal_oxides

Scandium

Scandium kangite https://en.wikipedia.org/wiki/Kangite

Titanium

Ti₂O₃ https://en.wikipedia.org/wiki/Tistarite

Titanium is common so not listed here. See: Rutile

Vanadium

VO₂, https://en.wikipedia.org/wiki/Vanadium_oxide
paramontroseite, orthrhombic, Mohs:?(likely mid hard),
https://en.wikipedia.org/wiki/Paramontroseite (transparent)

Chromium

https://en.wikipedia.org/wiki/Chromium_oxide

CrO https://en.wikipedia.org/wiki/Chromium(II)_oxide

Cr₂O₃, https://en.wikipedia.org/wiki/Chromium(III)_oxide
https://en.wikipedia.org/wiki/Eskolaite (trigonal, Mohs 8.0 to 8.5)

CrO₂, https://en.wikipedia.org/wiki/Chromium(IV)_oxide
rutile structure; are there natural minerals? Always opaque?

CrO₃ https://en.wikipedia.org/wiki/Chromium_trioxide

Manganese

MnO₂, sutile structure, https://en.wikipedia.org/wiki/Pyrolusite
Always opaque?
https://en.wikipedia.org/wiki/Manganese_dioxide (tetragonal, Mohs 6.0 to 6.5)
https://en.wikipedia.org/wiki/Ramsdellite (orthorhombic, Mohs 3)
https://en.wikipedia.org/wiki/Akhtenskite (hexagonal, Mohs ?)

Iron

Iron is common so not listed in detail here.

https://en.wikipedia.org/wiki/Iron_oxide
FeO https://en.wikipedia.org/wiki/W%C3%BCstite (rock salt structure, Mohs 5.0 to 5.5)
FeO https://en.wikipedia.org/wiki/Iron(II)_oxide
Fe₃O₄ https://en.wikipedia.org/wiki/Magnetite
Fe₂O3₄ https://en.wikipedia.org/wiki/Hematite

Cobalt

https://en.wikipedia.org/wiki/Cobalt_oxide CoO https://en.wikipedia.org/wiki/Cobalt(II)_oxide
https://en.wikipedia.org/wiki/Cobalt(II,III)_oxide

Nickel

https://en.wikipedia.org/wiki/Nickel_oxide

NiO https://en.wikipedia.org/wiki/Nickel(II)_oxide
NiO https://en.wikipedia.org/wiki/Bunsenite (rock salt structure, Mohs 5.5)

NiFe2O4 https://en.wikipedia.org/wiki/Trevorite (iron rich, cubic, Mohs 5)

Copper

https://en.wikipedia.org/wiki/Copper_oxide

Cu₂O https://en.wikipedia.org/wiki/Copper(I)_oxide
https://en.wikipedia.org/wiki/Cuprite (transparent, Mohs 3.5 to 4.0)

CuO https://en.wikipedia.org/wiki/Copper(II)_oxide
https://en.wikipedia.org/wiki/Tenorite (monoclinic, Mohs 3.5 to 4.0)

Zinc

https://en.wikipedia.org/wiki/Zinc_oxide https://en.wikipedia.org/wiki/Zincite (transpatent, hexagonal, Mohs 4)

Transition metal nitrides

Scandium

ScN, scandium nitride, https://en.wikipedia.org/wiki/Scandium_nitride
"indirect bandgap of 0.9 eV and direct bandgap of 2 to 2.4 eV"

Group 13 boron =

Many very hard and high performance materials here. Manny allotropes and polymorphs.

Group 13 beyond extremely abundant aluminum

Compounds with one of the main components being one of Ga, In, Tl

Group 14 beyond Si

Compounds with one of the main components being one of Ge, Sn, Pb

Group 15 beyond P (heavy pnictogens)

Compounds with one of the main components being one of As, Sb, Bi

Group 16 beyond S (heavy chalkogenides)

Compounds with one of the main components being one of Se, Te, (Po)

Other

Group 1 & 2 top rare: Lithium and Beryllium

BeO https://en.wikipedia.org/wiki/Bromellite

https://en.wikipedia.org/wiki/Lithium_oxide

Related

• Gemstone
• Oddball compound