African opal, 2.428 carats

Technical details: Type: African Opal (Opal) Weight: 2.428 carats Shape: Pear Color: Black Clarity: Unclassified (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 (amorphous) 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 various spectral colors change with the viewing angle, due to light interference with 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.