Kyanite
Kyanite is a mineral named by Werner in 1790, and is a polymorph of andalusite and sillimanite, sharing the same chemical composition. Often showing a vibrant blue color, it is known as "Aishoseki" (blue crystal stone) in Japan. Because of its unique property of possessing two different hardnesses, it is also called "disthene" or "dual-hardness stone."
Kyanite with its beautiful, vibrant blue color
Basic Information
| English Name | Kyanite |
|---|---|
| Japanese Name | Aishoseki (藍晶石) |
| Chemical Formula | Al2[O|SiO4] |
| System | Triclinic |
| Hardness | 4/4.5 on the main axis, 7.5 on the side axis (Dual-hardness) |
| Specific Gravity | Approx. 3.6 |
| Transparency | Transparent to translucent |
Features & Variations
- Kyanite Cat's Eye: Shows a chatoyancy effect due to dense tubular inclusions.
- Bicolor Kyanite: Different colors, such as green and blue, yellow and blue, or colorless and blue, appear in a single crystal.
- Orange Kyanite: Crystals colored entirely orange by Mn (manganese) were recently discovered in Myanmar.
- Star Kyanite: Forms a cross-shaped star due to the combination of chrysotile and reflections from the cleavage planes.
Origins, Aliases, Treatments, & Similar Stones
Main Origins: Nepal, Myanmar, Brazil, India.
Aliases: Sapphire three, blue talc, Nepal sapphire.
Treatments: Resin impregnation (to reinforce internal fractures), dyeing (infusing dye into cracks along cleavage planes).
Similar Stones: Blue sapphire, tourmaline (distinguished by specific gravity, presence of twinning, and cleavage state).
Note: Kyanite is a blade-like crystal with color banding and well-developed cleavage planes, making it prone to breakage. Oil is sometimes used to fill cracks to make them less visible. Because it is fragile, it is safer to avoid wearing kyanite or emerald necklaces.