Zircon

Chemical Formula

ZrSiO₄

Composition

Zirconium silicate, often with some hafnium and occasionally with some uranium, thorium, and yttrium. It can contain up to 20 percent of hafnium in its structure; if it exceeds that amount then it is no longer Zircon but Hafnon.

Variable Formula

(Zr,Hf)SiO₄ ;
(Zr,Hf,U,Th,Y)SiO₄

Color

The most common color is dark brown. Also black, gray, light brown, brownish-red, orange, pink, yellow, light blue, light green, light purple white, and colorless. Sometimes multicolored black and dark red, or multicolored with lighter and darker streaks.

Streak

Colorless

Hardness

7.5

Crystal System

Tetragonal

Crystal Forms 
and Aggregates

As short and stubby crystals, as well as prismatic which are sometimes elongated. Crystals are almost always terminated with a pyramidal termination. Crystals may be doubly terminated, and occasionally entirely pyramidal resembling an octahedron. Also grainy, as fibrous aggregates, and as rounded, waterworn pebbles. Twinned Zircon crystals are uncommon but do exist. Crystals can also be in a metamict where they exhibit rounded crystal faces.

Transparency

Transparent to opaque

Specific Gravity

4.6 - 4.8

Luster

Greasy to adamantine. Radioactive Zircon has a pitchy luster.

Cleavage

3,2

Fracture

Conchoidal to uneven

Tenacity

Brittle

Other ID Marks

May be fluorescent orange-yellow in shortwave ultraviolet light.
 

In Group

Silicates; Nesosilicates

Striking Features

Crystal shape, hardness, and weight

Environment

Most often in igneous environments, usually in granite pegmatites and in nepheline syenite pegmatites. Also in high-grade metamorphic rocks and in placer deposits.

Rock Type

Igneous, Metamorphic

Popularity (1-4)

1

Prevalence (1-3)

2

Demand (1-3)

1