| Mineral | Chemical formula | Crystal system | Mohs hardness | Density |
|---|---|---|---|---|
| Xanthiosite | Ni₃(AsO₄)₂ | Monoclinic | 4.0 | 5.56 g/cm³ |
| Xanthoconite | Ag₃AsS₃ | Monoclinic | — | 5.39 g/cm³ |
| Xanthoxenite | Ca₄Fe³⁺₂(PO₄)₄(OH)₂·3H₂O | Triclinic | — | — |
| Xenophyllite | Na₄Fe₇(PO₄)₆ | Triclinic | — | — |
| Xenotime-(Gd) | Gd(PO₄) | Tetragonal | — | — |
| Xenotime-(Y) | Y(PO₄) | Tetragonal | — | 4.27 g/cm³ |
| Xenotime-(Yb) | Yb(PO₄) | Tetragonal | — | 6.56 g/cm³ |
| Xiangjiangite | Fe³⁺(UO₂)₄(PO₄)₂(SO₄)₂(OH)·22H₂O | Tetragonal | — | — |
| Xianhuaite-(Ce) | K₂CeNb₅O₁₅ | Tetragonal | — | — |
| Xianhuaite-(La) | K₂LaNb₅O₁₅ | Tetragonal | — | — |
| Xieite | Fe²⁺Cr₂O₄ | Orthorhombic | — | — |
| Xiexiandeite | SiO₂ | Monoclinic | — | 2.63 g/cm³ |
| Xifengite | Fe₅Si₃ | Hexagonal | — | — |
| Xilingolite | Pb₃Bi₂S₆ | Monoclinic | — | 6.96 g/cm³ |
| Ximengite | Bi(PO₄) | Trigonal | — | 6.87 g/cm³ |
| Xingzhongite | Pb²⁺Ir³⁺₂S₄ | Cubic | — | — |
| Xitieshanite | Fe³⁺(SO₄)Cl·6H₂O | Monoclinic | — | — |
| Xocolatlite | Ca₂Mn⁴⁺₂Te⁶⁺₂O₁₂·H₂O | Monoclinic | — | — |
| Xocomecatlite | Cu₃(Te⁶⁺O₄)(OH)₄ | Orthorhombic | 4.0 | — |
| Xonotlite | Ca₆Si₆O₁₇(OH)₂ | Monoclinic | — | — |
| Xuite | Ca₃Fe₂[AlO₃(OH)]₃ | Cubic | — | — |
| Xuwenyuanite | Ag₉Fe³⁺Te₂S₄ | Cubic | — | — |