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• opal
  opal

  noun

  a mineral, an amorphous form of silica, SiO 2 with some water of hydration, found in many varieties and colors, including a form that is milky white.
• Opal
  Opal

  noun

  a female given name.

opal

¹ American  

[oh-puhl] / ˈoʊ pəl /

noun

1. a mineral, an amorphous form of silica, SiO 2 with some water of hydration, found in many varieties and colors, including a form that is milky white.

2. an iridescent variety of this that is used as a gem.

3. a gem of this.

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Opal ² American  

[oh-puhl] / ˈoʊ pəl /

noun

1. a female given name.

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opal British  

/ ˈəʊpəl /

noun

1. an amorphous, usually iridescent, mineral that can be of almost any colour, found in igneous rocks and around hot springs. It is used as a gemstone. Composition: hydrated silica. Formula: SiO 2 . n H 2 O

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opal Scientific  

/ ō′pəl /

1. A usually transparent mineral consisting of hydrous silica. Opal can occur in almost any color, but it is often pinkish white with a milky or pearly appearance. It typically forms within cracks in igneous rocks, in limestones, and in mineral veins. It also occurs in the silica-rich shells of certain marine organisms. Chemical formula: SiO ₂ ·nH ₂ O.

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Usage

What does opal mean? An opal is a gemstone that’s best known for its iridescent, milky-white variety. Other varieties are black and gray, but it can be almost any color. As a mineral, opal is a form of silica. Unlike many of the other gemstones used in jewelry, opal is not crystalline, meaning it does not form in a crystal structure—it looks like a stone, as opposed to a faceted jewel like a diamond. Opal gemstones are classified as common or precious. Precious is a label given to certain gemstones that are high in value. Opals labeled precious are typically those that display a high level of iridescence. Opal is the traditional birthstone for the month of October. It is associated with the zodiac signs Libra and Scorpio. Example: The opal pendant had flecks of green, pink, and blue.

Other Word Forms

• opal-like
  adjective

Etymology

Origin of opal

1350–1400; Middle English < Latin opalus < Greek opállios opal, gem; probably from a source akin to Sanskrit upala precious stone

Explanation

An opal is a gem, a semi-precious stone that comes in many shimmery, partly translucent colors. If your birthday is in October, an opal is your birthstone. An opal is a mineral made of silica, and it's found within the cracks and notches of many different kinds of rock. Most of the world's supply of opals comes from Australia. A polished opal that's been set in a ring or necklace is usually several shades or colors — most often blues and greens — with sparkles or shimmers decorating the stone. The word opal comes from the Latin opalus, and its ultimate root is probably the Sanskrit upala, "precious stone."

Example Sentences

We heard from a mother, Opal Foster, whose 18-year-old son has Down syndrome and lives at home as he strives to become a chef.

From Salon • Apr. 29, 2026

Opal does not give schools the ability to view a student’s activity within apps, Schlenker said.

From Los Angeles Times • Dec. 31, 2025

Deputy Chief Constable Jayne Meir, the NPCC's first lead for freight crime, said a new team at Opal - a police intelligence unit tackling organised acquisitive crime - would start targeting the issue next year.

From BBC • Nov. 17, 2025

Santos said a software issue affecting safety systems on board the BW Opal floating production storage and offloading unit had led to an unplanned shutdown of around two weeks last month.

From The Wall Street Journal • Oct. 16, 2025

What would the king do to Opal and her family if she didn’t spin the straw into gold?

From "Rump: The (Fairly) True Story of Rumpelstilskin" by Liesl Shurtliff