Chocolate Opal

Chocolate opal is a variety of the common opal, distinguished by its rich, dark brown color that often resembles the hue of chocolate. Like other opals, it is a form of hydrated silicon dioxide. The characteristic brown color comes from the presence of organic compounds or iron oxide within the stone. Chocolate opal displays a range of color play, often showing flashes of green, red, blue, and orange, depending on the light and angle of viewing.

“Chocolate” Opal Egg. Ethiopia. … Lapidary Art Eggs and Spheres | Heritage Auctions (ha.com)

Origin of the Name: The name “chocolate opal” directly references its distinctive brown color, reminiscent of dark or milk chocolate. The term “opal” itself derives from the Sanskrit word “upala,” which means “precious stone,” and later influenced by the Greek term “opallios,” meaning to see a change of color, referring to the unique color play that opals exhibit.

Overview of Opal Varieties, Highlighting Chocolate Opal: Opals are broadly categorized into various types based on their color characteristics and internal structure. Here are a few notable varieties:

1. White Opal: Common and showcases a pale white or light background with play-of-color.
2. Black Opal: The most valuable type, featuring a dark body tone which can be black, dark blue, or grey, enhancing the vibrancy of the color play.
3. Fire Opal: Known for its bright orange, red, or yellow body color, which may or may not exhibit color play.
4. Boulder Opal: Found embedded in ironstone boulders, where slices of opal are interspersed with the host rock, creating a unique pattern.
5. Chocolate Opal: This variety stands out due to its deep brown base color, offering a stunning and less common backdrop for the opal’s characteristic color play.

Chocolate opal is primarily found in Ethiopia, known for its rich deposits of high-quality opals. Ethiopian chocolate opals are prized for their unique appearance and vibrant color flashes, making them a popular choice among collectors and jewelry enthusiasts. They offer an aesthetic that differs significantly from the more common white or black opals, providing an appealing alternative for those seeking something unique in their jewelry or gemstone collections.

Contents

• Geological Formation of Chocolate Opal
• Physical and Optical Properties of Chocolate Opal
• Uses
• Major mining areas for Chocolate Opal

Geological Formation of Chocolate Opal

Natural Chocolate Opal – Crazicarma’s Crystals (crazicarmascrystals.com)

How Chocolate Opal is Formed: Chocolate opal forms through a sedimentary process. Silica-rich water percolates through the ground, filling cracks, voids, or between layers of rock. Over time, the silica particles deposit out of solution, assisted by the evaporation of water and changes in pressure and temperature. This deposition forms opal as the silica particles gradually accumulate into a gel, which then hardens. In the case of chocolate opal, the presence of organic material or iron oxide during formation gives it its characteristic brown color. The play-of-color is due to the internal structure of the opal, which diffracts light to display various colors depending on the conditions of viewing.

Typical Geographical Locations: Chocolate opals are prominently found in Ethiopia, particularly in the Wollo Province. This region is renowned for its opal mines, which yield a variety of opal colors including the distinctive chocolate opals. The deposits in Wollo are relatively recent discoveries, coming to prominence in the early 1990s, and have since produced a significant portion of the world’s supply of high-quality opals.

Differences Between Chocolate Opal and Other Types of Opal: Chocolate opal differs from other opal varieties primarily in its color and the conditions under which it forms:

1. Color and Appearance: The most distinguishing feature of chocolate opal is its deep brown body color, which contrasts with the white or light base of common opals or the dark, almost black, background of black opals. The brown color of chocolate opals can range from light milk chocolate to a darker, richer brown.
2. Play-of-Color: While all opals may exhibit a play-of-color, the effect is more pronounced in some types than others. Black opals, with their dark base, often display the most vivid colors, making them highly prized. Chocolate opals also show a vibrant play-of-color, which can be enhanced by their unique background color.
3. Geological Formation: The specific environmental and geological conditions of the Wollo region contribute to the formation of chocolate opal, with the presence of organic materials or iron oxides being crucial in defining its color. In contrast, other types of opal might form in different rock formations or without the presence of these coloring agents.
4. Rarity and Value: Black opals are the rarest and most valuable, primarily due to their dramatic appearance and striking color contrasts. Chocolate opals, while not as commonly found as white or crystal opals, hold a special place due to their unique aesthetic and are sought after by collectors and jewelry makers.

These differences make chocolate opal a unique and fascinating gemstone, offering an alternative to more traditional opal types while maintaining the enchanting qualities that make opals so beloved.

Physical and Optical Properties of Chocolate Opal

Ethiopian Chocolate Opal – Yita Ridge – FossilEra.com

Chocolate opal shares many of the general characteristics of opals but also exhibits unique physical and optical properties due to its specific composition and structure. Here’s an overview:

Physical Properties:

1. Hardness: Opals generally have a hardness of about 5.5 to 6.5 on the Mohs scale, making them relatively softer compared to many other gemstones. This hardness level suggests that while opals are durable enough for various types of jewelry, they require careful handling to avoid scratches and abrasions.
2. Specific Gravity: The specific gravity of opals ranges from about 1.98 to 2.25. Chocolate opals fall within this range, though the presence of additional elements like iron oxides might slightly alter their density.
3. Fracture: Opals typically exhibit a sub-conchoidal to uneven fracture. They can be brittle and may be prone to cracking under stress, especially when exposed to sudden changes in temperature or humidity.
4. Porosity: Opals can be somewhat porous, which affects their ability to absorb and retain water. This trait is crucial because dehydration can lead to crazing (the development of a network of fine cracks), which can diminish the gemstone’s aesthetic appeal and structural integrity.

Optical Properties:

1. Color Play (Play-of-Color): The most notable optical characteristic of opal is its ability to display a range of colors when light interacts with the microscopic spheres of silica gel within the stone. These spheres diffract light, showing various spectral colors. The specific colors and patterns depend on the arrangement and size of the silica spheres. Chocolate opals are particularly admired for their vibrant flashes of green, red, blue, and orange against their dark brown backdrop.
2. Body Color: Unlike other opals, the body color of chocolate opals is a distinctive brown, ranging from light to dark shades. This color is due to organic compounds or the presence of iron oxide within the stone, which differentiates it from the lighter hues of white opals or the dark tones of black opals.
3. Transparency: Chocolate opals can vary from opaque to translucent. The degree of transparency can affect the visibility of color play and also influences the stone’s overall luminosity and depth.
4. Refractive Index: The refractive index of opals generally ranges from about 1.37 to 1.52. This measure impacts how much light is bent when entering the stone, contributing to the opal’s unique visual effects. The refractive index can vary slightly among different opal types due to variations in their internal structures and compositions.

These properties make chocolate opals both challenging and rewarding to work with in jewelry. They require careful setting and maintenance to preserve their natural beauty and structural integrity. Their unique color play and rich body color offer a distinctive aesthetic that is highly valued in the gemstone market.

Uses

Chocolate opals, like other varieties of opal, are primarily used in the jewelry industry but also have applications in other decorative arts.

Jewelry

The most common use of chocolate opal is in fine jewelry. Due to their unique and appealing color play and intriguing chocolate hues, these opals are particularly favored for:

• Rings and Pendants: The striking appearance of chocolate opal makes it an excellent centerpiece for rings and pendants. These pieces often feature large, polished stones to showcase the opal’s color variations.
• Earrings and Bracelets: Smaller stones are frequently used in earrings and bracelets, where multiple opals can be set together to create a vibrant display of color and texture.
• Brooches and Other Ornaments: Chocolate opal can also be featured in brooches, tie pins, and other decorative jewelry items where its unique color can stand out.

Art and Decoration

Beyond jewelry, chocolate opals can be used in various artistic and decorative applications:

• Sculptures and Carvings: Skilled artisans may carve opals into intricate sculptures or decorative objects. The natural play of color in chocolate opal adds an extra dimension to such artworks.
• Inlays and Mosaics: Opals can be used as inlays in furniture, musical instruments, and other luxury items. Chocolate opal, in particular, provides a warm, rich color that is uncommon in other gemstones used for inlay work.

Collecting and Investment

Opals are also popular among collectors:

• Gemstone Collections: Due to their distinctiveness and beauty, chocolate opals are prized additions to gemstone collections.
• Investment: Some individuals purchase high-quality chocolate opals as an investment, betting on the gemstone’s rarity and demand to increase over time.

Metaphysical Uses

In the realm of metaphysical beliefs and crystal healing:

• Emotional Healing: Opals are believed to be stones of inspiration which enhance imagination and creativity. Chocolate opal, with its earthy tones, is sometimes associated with grounding and calming properties, helping to balance emotional states.
• Spiritual Work: Some practitioners use chocolate opals for spiritual endeavors, claiming that these stones facilitate personal transformation and assist in accessing one’s inner wisdom.

While the primary market for chocolate opals remains in jewelry, their appeal in various forms—from personal adornment to metaphysical uses—demonstrates their versatility and enduring allure. The unique characteristics of chocolate opal, especially its captivating color play against a rich brown backdrop, ensure that it continues to be a sought-after gem in various fields.

Major mining areas for Chocolate Opal

The major mining areas for chocolate opal are predominantly located in Ethiopia, particularly within the Wollo Province. This region has emerged as a significant source of opals, including the unique chocolate opal, since its discovery in the early 1990s. Here’s a closer look at the primary locations:

Wollo Province, Ethiopia

Wollo Province has become synonymous with high-quality opal mining in Ethiopia. The opal fields here are known for producing an array of opal types, with chocolate opal being one of the more distinctive varieties found. Key mining areas in Wollo include:

• Stayish Mine: Located near the town of Gashena, the Stayish mine is a prominent source of black opal and has also produced notable quantities of chocolate opal. This mine has been a significant contributor to the global opal market since its relatively recent development.
• Mezezo Opal Field: Although better known for its high-quality precious opals with vibrant play-of-color, Mezezo has also yielded chocolate opals. The opals from Mezezo are prized for their strong color play and durability.

These regions benefit from favorable geological formations where volcanic activity has contributed to the formation of opal through the deposition of silica-rich solutions into the surrounding rock. The unique conditions in these areas allow for the formation of the distinctive color and qualities of chocolate opal, making them crucial to its supply.

Other Potential Sources

While Ethiopia remains the dominant source, particularly the Wollo Province, there may be less well-documented or emerging sources in other opal-producing countries like Australia or Brazil. However, these have not yet become significant suppliers of chocolate opal specifically.

The mining areas in Ethiopia, especially around Wollo, continue to be explored and developed, contributing to both local economies and the global gemstone market. These mines are critical for enthusiasts and collectors seeking chocolate opal for its unique aesthetic qualities.