| oboyerite | H6Pb6(TeO3)3(TeO6)2·2H2O |
| obradovicite | H4(K,Na)CuFe2AsO4(MoO4)5·12H2O |
| obsidian | amorphous volcanic glass |
| o'danielite | NaH2(Zn,Mg)3(AsO4)3 |
| odinite | (Fe3+,Mg,Al,Fe2+)2.5(Si,Al)2O5(OH)4 |
| odintsovite | K2Na4Ca3Ti2Be4Si12O38 |
| oenite | CoSbAs |
| offretite | CaKMgAl5Si13O36·16H2O |
| ogdensburgite | Ca2(Zn,Mn)Fe4(AsO4)4(OH)6·6H2O |
| ohmilite | Sr3(Ti,Fe)Si4O12(O,OH)·2-3H2O |
| ojuelaite | ZnFe2(AsO4)2(OH)2·4H2O |
| okanoganite-(Y) | (Na,Ca)3(Y,Ce)12Si6B2O27F14 |
| okenite | Ca10Si18O46·18H2O |
| okhotskite | Ca2(Mn,Mg)(Mn,Al,Fe)2Si3O10(OH)4 |
| oldhamite | (Ca,Mg,Fe,Mn)S |
| olekminskite | Sr(Sr,Ca,Ba)(CO3)2 |
| olenite | NaAl3Al6(BO3)3Si6O18(O,OH)4 |
| olgite | Na(Sr,Ba)PO4 |
| oligoclase | (Na,Ca)(Al,Si)4O8 |
| olivenite | Cu2AsO4OH |
| olivine group | |
| olkhonskite | (Cr,V)2Ti3O9 |
| olmsteadite | KFe2(Nb,Ta)(PO4)2O2·2H2O |
| olsacherite | Pb2SeO4SO4 |
| olshanskyite | Ca3B4(OH)18 |
| olympite | LiNa5(PO4)2 |
| omeiite | (Os,Ru)As2 |
| omphacite | intermediate between aegirine, augite, jadeite |
| onoratoite | Sb8O11Cl2 |
| oosterboschite | (Pd,Cu)7Se5 |
| opal | SiO2·nH2O |
| orangite | thorite |
| orcelite | Ni5-XAs2 |
| ordonezite | ZnSb2O6 |
| orebroite | Mn3(Sb,Fe)Si(O,OH)7 |
| oregonite | Ni2FeAs2 |
| orickite | 2CuFeS2·H2O |
| orientite | Ca2MnMn2Si3O10(OH)4 |
| orlymanite | Ca4Mn3Si8O20(OH)6·2H2O |
| orpheite | H6Pb10Al20(PO4)12(SO4)5(OH)40·11H2O |
| orpiment | As2S3 |
| orschallite | Ca3(SO3)2SO4·12H2O |
| orthobrannerite | UUTi4O12(OH)2 |
| orthochamosite | (Fe2+,Mg,Fe3+)5Al(Si3Al)O10(OH,O)8 |
| orthochrysotile | Mg3Si2O5(OH)4 |
| orthoclase | KAlSi3O8 |
| orthoericssonite | BaMn2FeSi2O8OH |
| orthojoaquinite-(Ce) | Ba2NaCe2FeTi2Si8O26(O,OH)·H2O |
| orthopinakiolite | (Mg,Mn)2MnBO5 |
| orthoserpierite | Ca(Cu,Zn)4(SO4)2(OH)6·3H2O |
| orthowalpurgite | (UO2)Bi4(AsO4)2O4·2H2O |
| osarizawaite | Pb2Cu2Al4(SO4)4(OH)12 |
| osarsite | (Os,Ru)AsS |
| osbornite | TiN |
| osmiridium | iridium |
| osmium | (Os,Ir,Ru) |
| osumilite | (K,Na)(Fe,Mg)2(Al,Fe)3(Si,Al)12O30 |
| osumilite group | |
| osumilite-(Mg) | (K,Na)(Mg,Fe)2(Al,Fe)3(Si,Al)12O30 |
| otavite | CdCO3 |
| otjisumeite | PbGe4O9 |
| ottemannite | Sn2S3 |
| ottrelite | (Mn,Fe,Mg)2Al4Si2O10(OH)4 |
| otwayite | Ni2CO3(OH)2·H2O |
| oulankaite | (Pd,Pt)5(Cu,Fe)4SnTe2S2 |
| ourayite | Ag3Pb4Bi5S13 |
| oursinite | (Co,Mg)(UO2)2Si2O7·6H2O |
| overite | CaMgAl(PO4)2OH·4H2O |
| overite group | |
| owensite | (Ba,Pb)6(Cu,Fe,Ni)25S27 |
| owyheeite | Ag2Pb7(Sb,Bi)8S20 |
| oxammite | (NH4)2C2O4·H2O |
| oyelite | Ca10Si8B2O29·12.5H2O |