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Mother of opal is a naturally occurring form of non-crystalline hydrated silica, distinguished from precious opal by its lack of play-of-color and characterized by its opaque, porcelain-like appearance. The material forms in sedimentary deposits through the precipitation of silica from groundwater, typically appearing in white, cream, or pale blue-gray hues.
The mineralogical composition consists primarily of silicon dioxide (SiO2·nH2O) with varying amounts of water content, ranging from 6% to 10%. Its microstructure features closely packed silica spheres in a regular array, but unlike precious opal, these spheres are either too irregular or too large to produce diffraction effects. The material exhibits a hardness of 5.5-6.5 on the Mohs scale and possesses a specific gravity between 1.9-2.2.
Geologically significant deposits occur in Australia’s Great Artesian Basin, particularly in Lightning Ridge and Coober Pedy, where the material forms in weathered sedimentary rocks. The substance serves as host material for precious opal and maintains industrial applications in ceramics and as an abrasive component.
Mother of opal is typically a natural gemstone.
Common names for Mother of Opal include: Opalite, Tiffany Stone, and Ice Cream Opal.
Mother of pearl, often associated with opal as “”mother of opal,”” generally has a Mohs hardness of around 2.5 to 4.5. This makes it relatively soft compared to many gemstones and susceptible to scratching.
The refractive index of mother of pearl ranges from approximately 1.52 to 1.69, depending on the specific type and the orientation of the crystals within the material.
Mother of pearl exhibits an iridescent luster known as ‘pearlescent’. The luster can vary from silky to submetallic in appearance.
Mother of pearl does not have a defined cleavage but can be split along the layers of the shell from which it is composed.
The fracture of mother of pearl is typically uneven or splintery, reflecting its organic and layered structure.
The specific gravity of mother of pearl is typically around 2.60 to 2.85, which is relatively light, indicative of its organic composition.
Mother of pearl has low to moderate double refraction, which can contribute to its iridescence. The exact value can vary depending on the specific arrangement of the crystalline structure.
Mother of pearl has very low dispersion and does not typically display fire like some other gemstones such as diamond.
Mother of pearl is composed of aragonite crystals, which are orthorhombic, organized in a layered structure within the organic matrix of the mollusk shell.
The color of mother of pearl can vary widely, including white, cream, silver, pink, green, and blue, often showing iridescent flashes of these colors together.
Mother of pearl is generally opaque but can have varying degrees of translucency depending on the thickness and treatment of the material.
Pleochroism is not typically observed in mother of pearl due to its opaque nature and the diffuse reflection of light from its surface.
Mother of pearl may exhibit weak fluorescence under ultraviolet light, but this is not a prominent feature of the material.
The toughness of mother of pearl is generally fair due to its organic and layered structure, making it somewhat durable but liable to cracking under pressure.
Mother of pearl is somewhat brittle, reflecting its organic composition and layered structure.
The optic sign of mother of pearl is typically isotropic due to its amorphous structure, though it can show birefringence due to the alignment of aragonite crystals.
Mother of pearl does not have a characteristic absorption spectrum that is used for identification purposes.
Mother of pearl is primarily composed of calcium carbonate in the form of aragonite, with conchiolin (an organic protein) binding the crystals together.
Chatoyancy is rarely observed in mother of pearl due to its structure, though similar visual effects can occur due to the layering of the material.
Asterism is not typically present in mother of pearl.
Iridescence is one of the most characteristic features of mother of pearl, caused by the diffraction of light passing through its fine layers of aragonite crystals.
Mother of pearl is non-magnetic.
As an organic material, mother of pearl is a poor conductor of electricity.
Mother of pearl is not radioactive.
