Your Purchases
Black opal body tone is the fundamental darkness level or background color inherent in precious opal, ranging from N1 (darkest) to N9 (lightest) on the standardized GIA grading scale. This intrinsic darkness determines the contrast and visibility of the opal’s play-of-color against its base.
Dark body tones (N1-N4) create the most valued black opals, originating primarily from Lightning Ridge, Australia. These specimens exhibit exceptional contrast between the dark body and brilliant spectral colors. The darkness results from trace elements and microscopic carbon inclusions within the opal’s silica structure, creating a natural phenomenon where light cannot easily penetrate the stone’s body.
The intensity of black body tone directly correlates with an opal’s ability to display vibrant color patterns. N1 and N2 grades, being the darkest classifications, provide optimal conditions for the diffraction and reflection of light, resulting in the most dramatic play-of-color displays against their near-black backgrounds.
Common names for Black opal body tone include Lightning Ridge Black Opal, Dark Opal, and Midnight Opal.
Black opal has a hardness of about 5.5 to 6.5 on the Mohs scale, which makes it relatively softer compared to many other gemstones. This level of hardness suggests that while black opal is somewhat durable, it can still be prone to scratches and requires careful handling.
The refractive index of black opal ranges from approximately 1.37 to 1.52. This property contributes to the stone’s unique play of color and its overall brilliance.
Black opal exhibits a subvitreous to waxy luster, which enhances its visual appeal by providing a gentle sheen on the surface that complements its vibrant color display.
Opal, including black opal, typically does not exhibit any cleavage, which is a term used to describe the way a mineral breaks along certain structural planes. Its amorphous structure means it breaks in a conchoidal or uneven pattern.
Black opal has a conchoidal or uneven fracture, which is typical for amorphous substances like opal. This type of fracture can result in a smooth surface on broken pieces.
The specific gravity of black opal ranges from about 1.98 to 2.25. This variation can be attributed to differences in impurities and water content within the stone.
Opal, including black opal, is isotropic and does not exhibit double refraction. This means that light passes through the gem without splitting into two rays.
Black opal is particularly famed for its dispersion, often referred to as “”fire””. This characteristic refers to the stone’s ability to disperse light into a spectrum of colors, contributing to its stunning visual appeal.
Opals, such as black opal, are amorphous, meaning they do not have a crystalline structure. This lack of a crystal system is what allows for the unique color play in opals.
Black opal can display a wide range of colors on a dark body tone, from vivid greens and blues to fiery reds and oranges. The dark body tone, which can range from dark gray to black, enhances the color play, making the colors appear more vibrant.
Black opals vary in transparency from opaque to translucent. The level of transparency can affect the value and appearance of the gemstone.
Black opal does not exhibit pleochroism due to its isotropic nature. This means that the color remains constant regardless of the viewing angle.
Some black opals may exhibit a weak to moderate fluorescence under ultraviolet light, typically showing green or white colors. However, fluorescence in black opal is not as commonly observed as in some other gem varieties.
Opal is generally categorized as a gem with fair to good toughness, but it can be susceptible to cracking and chipping due to its relatively low hardness and inherent internal stresses.
Black opal is brittle, which means it can break or chip relatively easily compared to more tenacious minerals.
As an isotropic material, black opal has an optic sign of “”isotropic””, indicating a single refractive index.
Black opal does not typically show a characteristic absorption spectrum due to its amorphous nature and variety of colors.
Black opal is a form of hydrated silica, SiO₂·nH₂O. Its water content can range from 3% to 21%, which significantly influences its physical properties.
While generally rare in black opal, chatoyancy or the cat’s eye effect can occasionally be observed in certain stones when cut en cabochon and aligned properly with the internal structure.
Asterism, or the star effect, is not commonly present in black opal.
One of the most cherished properties of black opal is its iridescence, showcasing spectacular color changes when the stone is viewed from different angles.
Black opal demonstrates no magnetism.
Being a type of silica, black opal is generally a poor conductor of electricity.
Black opal is not radioactive and poses no health hazards in this regard.
Black opals, with their mesmerizing color play and unique appearance, are truly one of nature’s most beautiful creations. Their care and handling require a gentle approach due to their physical properties.
