If it’s blue and bladed, it’s kyanite. Sometimes also if it’s white and bladed, or gray and bladed.
Kyanite is a polymorph of andalusite and sillimanite. These three minerals share the same formula, but are stable at different P/T conditions.
Physical Properties |
|
| Chemical formula | Al2SiO5 |
| Class | Nesosilicate Isolated tetrahedra |
| Crystal system | Triclinic |
| Habit | Bladed Tabular Parallel or radiating aggregates |
| Color | Blue to white |
| Hardness | 5 to 7 |
| Specific gravity | 3.6 |
| Cleavage | Two prominent: Perfect (100), good (010) |
| Fracture | Uneven |
| Luster | Vitreous Pearly |
| Transparency | Transparent to translucent |
| Streak | White |
Optical Properties |
|
| PPL | Typically colorless May be weakly blue and pleochroic High relief |
| XPL | High relief 1st order interference colors |
| δ | 0.016 |
| after Perkins, 344-345 |
Kyanite in Hand Sample
Kyanite
Blue kyanite speckled with garnet and chalcopyrite
Kyanite quartzite
Scanning electron micrograph of kyanite
Kyanite in Thin Section
Thin Section GigaPans
Kyanite quartzite, plane polars
Kyanite quartzite, crossed polars
