ZrSiO 4 Composition Zirconium silicate, often with some hafnium and occasionally with some uranium, thorium, and yttrium. When impure can be as low as 6 . Most often as short, stubby , prismatic crystals, which are almost always terminated .
Crystals also occur in elongated , terminated prisms.
Doubly terminated crystals are not uncommon. Radioactive zircon is characterized by rounded crystal faces. Zircon also occurs as grains , as fibrous aggregates, and as rounded, waterworn pebbles. Twinned Zircon crystals are uncommon. Transparency Transparent to opaque Specific Gravity 4.6 - 4.8 Luster Greasy to adamantine.