Kyanite is a unique natural refractory mineral whose crystal structure and physical properties make it important for both industrial and jewellery applications. The following is a detailed description of the crystal structure of kyanite:
Chemical Composition:
With the chemical formula Al2SiO5, kyanite is composed of aluminium oxide (Al2O3) and silicon dioxide (SiO2), with specific percentages of 63.1% aluminium oxide and 36.9% silicon dioxide. This chemical combination gives blue fused silica its high refractoriness and mechanical strength.
Crystal structure:
The crystal structure of kyanite belongs to the triclinic crystal system, the crystal habit is usually columnar or razor-sharp, and the single crystals are often in the form of long plates parallel to (100). This structure causes the physical properties of kyanite to vary in different directions, especially hardness.
Physical properties:
- HARDNESS: The hardness of kyanite varies markedly in different directions; this is known as anisotropy. On a fully developed cleavage plane the hardness is 4 to 5, while in the direction of vertical crystal extension the hardness is 6 to 7.
- Specific gravity: kyanite has a specific gravity of about 3.53 to 3.64.
- Disintegration: Disintegration of kyanite is complete in the (100) direction, while it is moderate to complete in the (010) direction.
- Fracture: kyanites are fragile and the fracture usually shows a glassy to pearly lustre.
- Colour: The colour of sapphire is usually blue, but can also be green, yellow, grey, brown or colourless due to the presence of impurities such as iron and chromium.
- Transparency: The clarity of blue sapphire can range from transparent to translucent.
- Lustre: Usually glassy.
Optical properties:
- Optical properties: kyanite crystals are inhomogeneous, biaxial crystals and negatively optical.
- Refractive index: The refractive index ranges from transparent to translucent.
- Lustre: Usually glassy.
Optical properties:
- Optical properties: kyanites are inhomogeneous, biaxial crystals and are negatively optical.
- Refractive index: The refractive index ranges from about 1.716 to 1.731.
- Birefringence: Birefringence between 0.012 and 0.017.
- UV fluorescence: Red colour in long wave UV, non-fluorescent in short wave UV.
- Absorption spectrum: absorption bands at 435nm and 445nm.
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Special optical effects:
Sapphire occasionally exhibits the cat’s eye effect, a rare optical phenomenon in which a bright band of light is created by reflected light from tiny internal needle-like inclusions.
Industrial applications:
Due to its resistance to high temperatures, chemical corrosion and thermal shock mechanical strength, blue shale is widely used in the manufacture of refractory materials such as indeterminate materials, top bricks for electric furnaces, phosphate unburnable bricks, mullite bricks and low creep bricks.
Gemological applications:
Sapphire is also used as a gemstone in the manufacture of jewellery such as rings, bracelets and necklaces. Switzerland and Austria are known sources of kyanite.
Industrial importance of crystal structure:
The crystal structure and physical properties of sapphire make it valuable in high-temperature industrial applications. For example, in steel production, blue shale is used as a refractory material to resist extreme heat and chemical attack. In addition, its thermal expansion properties are used in the manufacture of ceramics and refractory bricks with specific thermal properties.
Environmental adaptability:
The crystalline structure of blue fused silica makes it stable in different environmental conditions, making it a reliable choice for a variety of industrial processes.
Conclusion:
The crystal structure and chemical composition of kyanite together determine its unique physical and optical properties, which not only make it indispensable for industrial applications, but also make it a popular gemstone in the jewellery market. With further study of the crystal structure of kyanite, more areas of application may be discovered, thus increasing its commercial value.