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Cordierite (Photo) [abbr. Crd ]

Year of discovery: 1813 (Großer Arber, Germany), 1883 (Japan)

Locality list: 433 localities of cordierite

• Mg₂Al₄Si₅O₁₈
• (Mg,Fe)₂Al₄Si₅O₁₈
• [Mg²⁺₂][Al₄Si₅O₁₈]^4-

• Class: Coriderite group
• Class: Cyclo-Aluminosilicate (Single ring)
• Soluble in: HCl
• Magnetism: Paramagnetic
• Substitution pseudomorph: Replaced by Muscovite or Paragonite. (Cerasite)

• Polymorph: Indialite (High temperature, Hexagonal)

• Mg => Fe: Sekaninaite (Series), Ferroindialite

• Color: Gray, Pale blue, where color changes from dark blue to pale blue in directions
• Streak: White
• Luster: Vitreous
• Diaphaneity: Transparent-Translucent

• Habit: Prismatic, Pseudohexagonal prism
• Twin: Intrusive twin to form pseudohexagonal prism

• Cleavage: Perfect on {100} and {001} (2 plane), Indistinct on {010} (1 plane)
• Hardness: 7-7.5
• Density: 2.7

• System: Orthorhombic
• Group: mmm, Cccm
• Lattice: a=17.1, b=9.7, c=9.4

Etymology: P.L.A.Cordier, French geologist