Opal is a hydrated amorphous form of silica (SiO 2 · n H 2 O); its water content may range from 3% to 21% by weight, but is usually between 6% and 10%. Due to the amorphous (chemical) physical structure, it is classified as a mineraloid, unlike crystalline forms of silica, which are considered minerals.

Feb 22, 2025 · Opal is a fascinating gemstone that’s not like other rocks. When you look at it, it sparkles with many colors, like a rainbow got trapped inside. That’s called ‘play-of-color,’ and it’s what makes identifying opals in a sea of different gems possible.

Mar 5, 2025 · Opal is a fascinating mineral known for its unique play of colors and diversity. There are many types of opal, each with distinct characteristics that make them special. For example, boulder opal, hyalite, and fire opal are all unique forms of this mineral.

Apr 11, 2019 · Opal is a mineraloid or crystalline form of silica. It is colorless when pure. The Precious forms of Opal occur in a wide variety of colors, including white, yellow, red, orange, green, black, and blue. Raw stones have a waxy, dull luster that polishes to a vibrant shine.

Opal is one of the world's most popular gemstones and the birthstone for the month of October. A nice precious opal can flash every color of the spectrum with an intensity and quality of color that surpasses the fire of diamond. The best opals command prices per carat that rival expensive diamonds, rubies, sapphires, and emeralds.

Mar 21, 2025 · Opal, silica mineral extensively used as a gemstone, a submicrocrystalline variety of cristobalite. In ancient times opal was included among the noble gems and was ranked second only to emerald by the Romans.

Opal is an October birthstone. Grids of silica spheres 0.2 microns in size create red play-of-color flashes. Opal contains up to 20% water trapped in its silica structure. The novel “ Anne of Geierstein ” gave opal a reputation of being unlucky.

Sep 15, 2024 · Opal gems are so unique you’ll need a special vocabulary to describe them. Learn all about the many opal varieties and how to evaluate them.

Aug 11, 2021 · Opal gemstones are hydrated silica crystals that form over millions of years. Learn about opal details, including stone meanings and symbolism, history, pricing, and value.

Opal is known for its unique display of flashing rainbow colors called play-of-color. There are two broad classes of opal: precious and common. Precious opal displays play-of-color, common opal does not.