K is for Kyanite
Kyanite is a metamorphic rock forming mineral. It’s name comes from the Greek word ‘kyanos’ meaning ‘blue’ which is the predominate color of the mineral. It is also known by the name disthene which comes from the Greek words for ‘two’ and ‘strong’ due to this mineral having two different Mohs hardness ratings depending on the axis of the mineral – 4.5-5 parallel to one axis, and 6.5-7 perpendicular to that axis.
While the mineral is predominately blue to violet, there are also other colors like orange or green. The mineral is fairly common with a beautiful crystal structure but gem quality findings are rare. The mineral contains a lot of inclusions which makes faceting the stone difficult. There are many imitation kyanite gems on the market, so buyer beware.
Kyanite has many industrial and commercial uses due to it being a refractory (heat resistant) mineral. It is used in many porcelain products where heat resistance is important, like on the insulator of a spark plug or in kiln shelving and kiln furniture. Kyanite is also used in the manufacture of abrasives like cutting wheels, not because it is an abrasive, but it acts as a binding agent allowing the abrasives to be formulated in the disk shapes. It also has uses in the automotive and railway industry in the manufacture of brake shoes and clutch liners.
The Hudson Institute of Mineralogy has a database with beautiful examples of kyanite crystals. I encourage you to look at this vast array of kyanite by clicking here.
The Smithsonian has a beautiful 7.43ct kyanite from Nepal on display. The faceted stone has a beautiful blue color and appears free of inclusions. You can see it here.