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Opal (Photo) [abbr. Opl ]

Year of discovery: Prehistoric (World), 1890 (Japan)

Locality list: 385 localities of opal

• SiO₂,nH₂O
• [SiO_x(OH)_4-2x]_n

• Classified as follows:
• Opal-CT: Mixture of Cristobalite and Tridymite
• Opal-C: Cristobalite
• Opal-A_G: Precious opal. Iridescent amorphous gem opal showing play of color
• Opal-A_N: Hyalite. Glassy amorphous

• Class: Oxide - Hydrate
• Variety: Menilite (Nodule)
• Insoluble in: HCl
• Fluorescence: UV excitation (Yellowish green)

• H₂O => (C,H,O,N,S): Melanophlogite
• H₂O => (C,H): Chibaite
• H₂O => C_XH_2X+2: Bosoite

• Color: Colorless, White (Opalescence), Iridescent (Play of color)
• Streak: White
• Luster: Vitreous
• Diaphaneity: Transparent-Opaque

• Habit: Glassy

• Cleavage: No
• Hardness: 5.5-6.5
• Density: 2.1

• System: Amorphous

Etymology: Opalus (Jewel) in Latin