African opal, 3.71 carats

Technical details: Type: African Opal (Opal) Weight: 3.71 Carats Shape: Cabochon Color: Black Clarity: Uncategorized Transparency: Opaque Hardness: 5.5-6.5 Treatment: Smoke Treated Origin: African Certification: Electronic certificate (PDF) from Saudi Laboratory (MT) - website (www.mtgl.com.sa) The Opal is a semi-precious (non-crystalline) mineral of Hydrated Silica, known for its great diversity in appearance. The most famous type is the Precious Opal, which features a unique optical phenomenon called play-of-color, where iridescent flashes of different spectral colors change with the viewing angle, due to light interference with arranged microscopic silica spheres. The common Opal does not show this phenomenon but comes in a variety of colors. Opal forms in cavities of sedimentary and volcanic rocks when silica-rich water solutions are deposited.