Boron nitride
This is Boron
boron is an element
boron is an element
Boron Nitride.
Boron
boron
Aluminium nitride is a compound.
You think probable to boron nitride (borazon); but other nitrides (of titanium, zirconium, vanadium, niobium, etc.) are also very hard. But no one equal the hardness of diamond.
K3N is not an element. It is a compound known as potassium nitride.
Boron is an element.
Boron is element #5 in the periodic table.