Zircon

Zircon is a mineral that has been newly added as a December birthstone. It has the interesting property of being able to be dated by the progress of metamictization, which is self-destruction caused by radioactive elements incorporated within the zircon. *There is an article that explains this in detail.

Because zircon can reveal the age at which its crystals were formed, it is often called "the world's oldest mineral." The oldest zircon seems to have been created about 4.4 billion years ago.


The following are high-end values and may be downgraded depending on the condition.
Name: Zircon
Japanese name: Hyacinth
Chemical composition: ZrSiO₄
Crystal system: Tetragonal system
Specific gravity: 4.6–4.7
Mohs hardness: 7.5
Cleavage: Indistinct
Luster: Adamantine to resinous
Transparency: Transparent to translucent
Refractive index: 1.925–1.984
Birefringence: 0.059–0.066
Color: Colorless, blue, red, green, etc.
Dispersion: 0.039