opaali

Opal, or opaali in some languages, is a hydrated amorphous form of silica (SiO2·nH2O) that ranges in color from milky white to transparent to brilliant hues. Its most distinctive feature is the play of color, produced when light interferes with the microscopic arrangement of silica spheres within the gem. The water content, typically about 3 to 21 percent by weight, influences its appearance and stability.

Formation occurs when silica-rich solutions fill voids in rocks such as volcanic ash beds or sedimentary formations. Over time, silica precipitates and traps water, creating opal. Australia dominates world production, with notable sources including the opal fields near Lightning Ridge for black opal and Coober Pedy for white and crystal opal. Other producers include Ethiopia, Mexico, the United States, Brazil, and Slovakia.

Varieties include precious opal, which displays play-of-color across its body, and fire opal, which is transparent to translucent with warm reds to oranges and may lack color play. Boulder opal forms when opal fills cracks or voids in ironstone or sandstone, often preserving a natural matrix. Opalite is a trade name for a glass that imitates opal; laboratory-grown synthetic opals also exist and can resemble natural stones.

In jewelry, opal is valued for its color and iridescence but is relatively soft (Mohs hardness about 5.5 to 6) and sensitive to dehydration and extreme temperature changes. Care recommendations include gentle cleaning with mild soap and water, avoiding ultrasonic cleaners, and storing in a humid environment to prevent cracking. Opal is associated with October as a birthstone in various traditionals lists and remains widely used in decorative and jewelry pieces.