Minerals: O
Obsidian
SiO
2
Oldhamite
(Ca,Mg,Fe,Mn,S)
Olivenite
Cu
2
(AsO
4
)(OH)
Olivine
(Mg,Fe)
2
SiO
4
Omeiite
(Os,Ru,As)
Opal
SiO
2
.nH
2
O
Orpiment
As
2
S
3
Osbornite
TiN
Osmium
Os
Otavite
CdCO
3
Owyheeite
(Ag,Pb,Sb,S)