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Åkermanite, Akermanite [abbr. Ak ]

Year of discovery: 1884 (World), 1974 (Japan)

Locality list: 2 localities of Åkermanite

• Ca₂MgSi₂O₇
• Ca₂(Mg,Al)(Si,Al)SiO₇
• [Ca²⁺₂][Mg²⁺][Si₂O₇]^6-

• Class: Melilite series < Melilite group
• Class: Sorosilicate

• Mg => Zn: Hardystonite
• Mg => Be: Gugiaite
• Mg => Al: Alumoåkermanite (Alumoakermanite)

• MgSi => AlAl: Gehlenite (Series)
• MgSi => BB: Okayamalite

• Color: Colorless, Gray, Green, Brown
• Streak: White
• Luster: Vitreous-Resinous
• Diaphaneity: Transparent-Translucent

• Habit: Short prismatic, Tabular, Cube with Octahedral faces
• Twin: {100}{001}

• Cleavage: Distinct on {001} (1 plane), Indistinct on {110} (2 planes)
• Hardness: 5.5
• Density: 3.0

• System: Tetragonal
• Group: (-4)2m, P(-4)2₁m
• Lattice: a=7.8, c=5.0

Etymology: Anders Richard Åkerman (Akerman) (1837-1922), Swedish metallurgist