Silicates: Zircon

Composition: ZrSiO₄; some hafnium substitutes for zirconium

Crystal system: Tetragonal; prismatic crystals terminated by pyramids

5.33.1
zircon crystals with nepheline

Properties:

• Vitreous to adamantine lustre
• Variable color; colorless, brown, grey, green or violet
• White streak
• Knife does not scratch (Mohs Hardness 7.5)
• High density
• Cleavage rarely apparent
• Smooth fracture
• Not ferromagnetic
• Does not react with hydrochloric acid (HCl)

Occurrence:

Zircon is an accessory mineral in many igneous and metamorphic rocks and also occurs in heavy mineral sand deposits.

5.33.2
zircon crystals with nepheline

Zircon is a significant industrial mineral used in the manufacture of refractories and is the preeminent source of zirconium and hafnium that are used in the construction and operation of nuclear reactors.