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Tridymite [abbr. Trd ]

Year of discovery: 1868 (Cerro San Cristóbal, Mexico), 1894 (Japan)

Locality list: 331 locality of tridymite

• SiO₂
• [Si⁴⁺][O₂]^4-

• Class: Tectosilicate
• Class: Oxide
• Fluorescence: Short UV excitation (Dark red)
• Phase transition: Transit to Cristobalite above 1470 degree.
• Phase transition: Formed on transition of heated β-Quartz above 870 degree.

• Polymorph: Quartz (α) (<573 degree, Trigonal)
• Polymorph: β-Quartz (573-870 degree, Hexagonal)
• Polymorph: Cristobalite (>1470 degree, Tetragonal)
• Polymorph: Coesite (2.0-10 GPa, 500-800 degree, Monoclinic)
• Polymorph: Stishovite (>10 GPa, 500-800 degree, Tetragonal)
• Polymorph: Mogánite (Moganite) (Monoclinic)

• Si => Ge: Argutite
• Si => Sn: Cassiterite
• Si => Ti: Rutile, Anatase, Brookite
• Si => Pb: Scrutinyite (α), Plattnerite
• Si => Mn: Pyrolusite (β), Ramsdellite (γ), Akhtenskite (ε)
• Si => V: Paramontroseite
• Si => Mo: Tugarinovite
• Si => U: Uraninite
• Si => Th: Thorianite
• Si => Ce: Cerianite-(Ce)
• Si => Se: Downeyite
• Si => Zr: Baddeleyite
• Si => Te: Tellurite, Paratellurite

• Color: Colorless, White
• Streak: White
• Luster: Vitreous
• Diaphaneity: Transparent-Translucent

• Habit: Hexagonal platy

• Cleavage: Indistinct on {0001} (1 plane), Imperfect on {1010} (3 planes)
• Hardness: 6.5-7
• Density: 2.3

• System: Triclinic, Pseudoorthorhombic, Pseudohexagonal (2PH, 10PH)
• Group: 1, F1
• Lattice: a=9.9, b=17.2, c=81.9, α=90.0, β=90.0, γ=90.0