Opal Gemstones

Precious opals are known for their beautiful iridescent phenomenon, often called play-of-color. Their body color can range from white to black, and they may be transparent, translucent, or opaque.

Opal is a hydrated silica mineral with the formula SiO₂·nH₂O. There are different varieties of opal, including precious opal, fire opal, boulder opal, and non-iridescent opal.

What Makes Opal Unique?

Unlike many crystalline gemstones, opal is made of closely packed silica spheres with water held within its structure. In precious opal, light passing through these tiny spheres can separate into spectral colors, creating play-of-color. The visible colors and patterns may change as the stone is moved under light.

Play-of-color is different from a stone's body color. Body color is the underlying background of the opal, while play-of-color is the flashing display of color seen across its surface. Common body colors include white, gray, black, orange, and clear or translucent material. You can compare these features across a wider range of loose gemstones for collectors.

Types of Opal

• Precious opal
• Fire opal
• Boulder opal
• Non-iridescent opal

Precious Opal

Precious opals have a beautiful iridescent phenomenon. Their main body color ranges from white to black, and they can be transparent to opaque.

Collectors often look at the brightness, range of colors, pattern, body color, and the way color is distributed across the face of a precious opal. A stone can show one color or a broad mix of colors, and each opal has its own individual pattern. For an October-birthstone perspective, read the guide to opal and tourmaline birthstones.

Fire Opal

Fire opal color ranges from brown to orange. Some fire opals may be iridescent.

Fire opal is valued for its warm yellow, orange, and reddish body colors. While some pieces show play-of-color, many are appreciated primarily for their clear to translucent orange body color. A fine example of a cut stone is this 3.6 carat oval Ethiopian opal cabochon.

Transparency: Transparent to opaque

Luster: Sub-vitreous

Refractive index (R.I.): 1.40 to 1.45

Specific gravity (S.G.): 2.2

Boulder Opal

These are also iridescent opals found in brown rock. The stone retains its brown mother rock.

Boulder opal is commonly cut with part of its natural ironstone host rock attached. This natural backing can create a dark background that helps make the opal's color display easier to see, while also making every finished piece distinct.

Non-Iridescent Opal

There are also opals that do not show play-of-color. They occur in different colors, such as green, pink, blue, and brown.

These materials are often described by their body color or appearance rather than by play-of-color. They can still be attractive collector stones because of their soft color, pattern, translucency, or cabochon-cut appeal. See how collectors approach selection in these frequently asked questions about buying loose gemstones.

Opal Care and Wearing Tips

Opal is generally softer than many commonly worn gemstones, with a Mohs hardness of about 5 to 6.5. It is best protected from hard knocks, scratching, sudden temperature changes, and harsh chemicals. Store opal jewelry separately from harder gems, and clean it gently with a soft cloth and mild soapy water when needed.

Because opal contains water, avoid prolonged exposure to very dry heat. Never use ultrasonic or steam cleaners unless a qualified professional has confirmed that the particular opal and its setting are suitable. If you are comparing individual stones, consider this 7.7 carat natural Ethiopian opal alongside its intended setting and use.

What to Consider When Buying Opal

• Color display: Look at brightness, the colors visible, and how the play-of-color appears as the stone moves.
• Pattern: Notice whether the color appears in broad flashes, small pinpoints, or another natural pattern.
• Body color: Consider whether you prefer a light, dark, orange, or translucent background.
• Cut and condition: A well-finished cut should present the color attractively. Check that the stone is appropriate for its intended use and setting.

Buyers who need multiple stones or calibrated material can also explore the store's wholesale loose gemstone selection.

Frequently Asked Questions About Opal

What is play-of-color in opal?

Play-of-color is the shifting display of spectral colors seen in precious opal when it is viewed or moved under light.

Do all opals show play-of-color?

No. Precious opal shows play-of-color, while non-iridescent opal does not. Some fire opals may show it, but many do not.

Can opal be worn in jewelry?

Yes. Opal can be worn in jewelry, but it benefits from thoughtful settings and careful everyday wear because it is relatively soft.