Kyanite

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

Kyanite, PPL

Kyanite, Plane Polars

Kyanite in quartzite, in plane polarized light. To view this mineral in crossed polars, click here: https://youtu.be/H4jcL7exIOI To explore this slide in pla…

Kyanite, XPL

Kyanite, Crossed Polars

Kyanite in quartzite, in plane polarized light. To view this mineral in plane polars, click here: https://youtu.be/aOsD_lRYWuc To explore this slide in plane polars, click here: https://viewer.gigamacro.com/view/xTYqmupFt7lI7nYw To explore a gigapan of this slide in crossed polars, click here: https://viewer.gigamacro.com/view/6TgFi0nJaqEdFjVD To explore a gigapan of a hand sample of kyanite, click here: https://viewer.gigamacro.com/view/UnbzlZe7tNYmjGLK NVCC slide AN 86.

Further Reading

Kyanite at webmineral.com
Kyanite at mindat.org