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Adularia (Photo) [abbr. Adl ]

A rhombic variety of Orthoclase formed at lower temperature. Its character is intermediate between Orthoclase and Microcline. Si-Al is ordered more than Orthoclase and less than Microcline.

Year of discovery: 1780 (Adula massif, Switzerland), 1900 (Japan)

Locality list: 283 localities of adularia

• Class: Alkaline Feldspar subgroup - Feldspar group
• Class: Tecto-Aluminosilicate
• Insoluble in: HCl, HNO₃, H₂SO₄

• Polymorph: Sanidine (Monoclinic, Formed above 650 degree, Disordered Si-Al)
• Polymorph: Orthoclase (Monoclinic, Formed between 300-650 degree, Intermediately ordered Si-Al)
• Polymorph: Microcline (Trilinic, Formed below 300 degree, Ordered Si-Al by annealing)

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

• Habit: Rhombohedral

• System: Monoclinic

Etymology: Adula Mountains, Switzerland