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Contra luz opal is a rare hydrated silica variety that exhibits a unique optical phenomenon where light passes through the transparent to translucent body of the opal, creating distinctive play-of-color patterns visible from both sides. The name derives from Spanish “”contra luz,”” meaning “”against the light,”” referring to its primary viewing method.
These opals form in volcanic regions where silica-rich solutions penetrate and fill cavities in host rocks. Their internal structure consists of uniformly sized spheres of silica arranged in a regular pattern, creating a three-dimensional diffraction grating that splits white light into spectral colors. The finest specimens originate from Mexico, particularly the Queretaro region, where geological conditions produce exceptional clarity and color play.
The distinguishing feature of contra luz opal lies in its transparency level, which allows light transmission through its entire body, unlike common opals that display color play only on their surface. These gems typically exhibit red, orange, and green flash patterns when viewed with transmitted light, with some specimens showing rare blue and violet hues.
Contra Luz Opal is typically a natural gemstone.
Common names for Contra Luz Opal include Cantera Opal, Mexican Opal, and Fire Opal when it exhibits a play-of-color against a light body color.
Contra Luz Opal generally has a hardness of about 5.5 to 6.5 on the Mohs scale, making it relatively softer compared to many other gemstones. This level of hardness makes it somewhat susceptible to scratches and abrasion.
The refractive index of Contra Luz Opal ranges from approximately 1.37 to 1.47. This property influences how much the light bends or refracts when entering the stone, playing a role in its visual effects.
Contra Luz Opal exhibits a subvitreous to waxy luster, which contributes to its unique visual appeal, showcasing a soft yet radiant glow from within.
This opal does not exhibit any natural planes of cleavage, which is typical for opals, meaning it does not readily split along any defined plane.
Contra Luz Opal commonly has a conchoidal fracture, resembling the curves seen on a seashell, which is typical for opals.
The specific gravity of Contra Luz Opal is typically within the range of 1.98 to 2.25, which can vary slightly depending on the exact composition and inclusions in the stone.
As an amorphous mineraloid, Contra Luz Opal does not exhibit birefringence or double refraction due to its lack of a crystalline structure.
This type of opal is known for its play of color or “”fire,”” which can show a broad spectrum of colors. The dispersion is relatively high, which contributes to its beautiful and striking appearance.
Opals, including Contra Luz Opal, are amorphous rather than crystalline. They do not belong to any crystal system.
Contra Luz Opal can display a clear to milky white base color, with vibrant play of color showing varied hues depending on the angle of light and observation.
Contra Luz Opals range from transparent to translucent, enhancing their depth and appeal through the play of light and color within the stone.
This property is not applicable to Contra Luz Opal as it is amorphous and does not exhibit pleochroism, which is typical for isotropic materials.
Some Contra Luz Opals may exhibit fluorescence under ultraviolet light, often showing green or other bright colors, depending on the specific qualities of the specimen.
Opals, including Contra Luz, are generally considered to have fair to poor toughness due to their internal structure, making them more vulnerable to cracking from impact.
Contra Luz Opal is generally brittle, which is a common characteristic of opal due to its microcrystalline composition.
Being isotropic, the optic sign of Contra Luz Opal is typically uniaxial and non-directional, owing to its amorphous nature.
Contra Luz Opal does not typically display a characteristic absorption spectrum due to its amorphous nature and variable composition.
Contra Luz Opal is a form of hydrated silica (SiO2·nH2O). The water content can range from 3% to 21% by weight, which significantly influences its properties.
While not common, some Contra Luz Opals can exhibit a cat’s eye effect when cut en cabochon and aligned properly with the internal structure.
Asterism or a star effect is generally not observed in Contra Luz Opal, as this effect is more typical of crystalline gemstones.
Contra Luz Opal is well-known for its iridescence, displaying a variety of colors that change and move with the light, known as the play-of-color.
Contra Luz Opal is not magnetic due to its siliceous nature and lack of ferromagnetic materials.
This opal is generally a poor conductor of electricity, consistent with its composition as a form of silica.
Contra Luz Opal is not radioactive and poses no health hazards related to radioactivity.
