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

The broth is still at the center of all things La Mer: Past celebrations have involved “broth-tinis,” which are just cocktails made to resemble the opal liquid with its root beer smell.

From The Wall Street Journal • Mar. 18, 2026

The array of fossils were found about 25 years ago by palaeontologist Elizabeth Smith and her daughter Clytie while they were going through the discards of an opal mine.

From BBC • May 27, 2024

The fossils were found by Elizabeth Smith and her daughter Clytie of the Australian Opal Centre in Lightning Ridge, who have spent decades working and searching over the opal fields.

From Science Daily • May 27, 2024

Authorities also gave her a gold ring set with an opal and two diamonds that was found with her mother’s remains.

From Seattle Times • Dec. 4, 2023

Bast leaned closer until their faces were mere inches apart, his eyes gone white as opal, white as a full-bellied moon.

From "The Name of the Wind" by Patrick Rothfuss