| Kalipyrochlore | (K,Sr,Nb,O,OH,nH2O) |
| Kaolinite | Al2Si2O5(OH)4 |
| Kamacite | (Fe, Ni) |
| Karelianite | (V,O) |
| Kempite | (Mg,Cl,OH) |
| Kermesite | Sb2OS2 |
| Kernite | Na2B4O6(OH)2.3H2O |
| Klockmannite | (Cu,Se) |
| Kolwezite | (Cu,Co)2(CO3)(OH)2 |
| Kolymite | Cu7Hg6 |
| Kostovite | (Cu,Au,Te) |
| Krennerite | (Ag,Au,Te) |
| Krutaite | (Cu,Se) |
| Kukharenkoite | Ba2Ce(CO3)3F |
| Kullerudite | (Ni,Se) |
| Kunzite | LiAl(SiO3)2 |
| Kutnohorite | Ca(Mn,Mg,Fe)(CO3)2 |