Zircon has been around since antiquity. Where it's name comes from is uncertain. It has a great brillance and intense fire due to its high refractive index and strong dispersion. It is sensitive to knocks and pressure, and edges are easily damaged. It contains a relatively high content of radioactive elements (uranium, thorium) causing large variation of pysical properities. A normal zircon (called high zircon) is one which has the highest values in optical properities. Ones with lower values are called low zircons.

• Color: Colorless, yellow, brown
  oarnge, red, violet, blue, green
• Color of streak: white
• Moh's Hardness : 6 1/2 - 7 1/2
• Specific gravity : 3.90 - 4.71
• Cleavage : Imperfect
• Fracture : Conchoidal, very brittle
• Crystal System : Tetragonal; short,
  four-prisms with pyramidal(Br>ends
• Chemical Composition : Zr(SiO4)
  zirconium silicate
• Transparency : Translucent
• Refractive Index : 1.777 - 1.987
• Double Refraction : +0.059 (none in
  green stones)
• Dispersion : 0.039
• Pleochroism : Yellow: very weak;
  honey, yellow-brown, yellow
  Red: very weak; red, light brown
  Blue: definate; blue, yellow, gray
  colorless
• Absorption spectrum: (normal) 6910,
  8690, 6625, 6605, 6535, 6210,
  6150, 5895, 5620, 5375, 5160,
  4840, 4600, 4327
• Fluorescence : Blue: very weak;
  light orange
  Red and brown; weak; dark yellow