Zircon

Zircon, zirconium (zirconium silicate) is a square mineral. The name derives from the Persian zargun - colored as gold, according to the color of one of the varieties. Zircon is the oldest known mineral on Earth (in relation to the age of the Earth, not to human knowledge); Most often occurs in the form of tabular to prismatic crystals, with a square cross-section, terminated by a quadrilateral pyramid

Color: colorless, yellow, green, blue ...
Crystal appearance: prismatic, dipyramidal
System: square
Hardness: 7.5
Gloss: Diamond
Fission: imperfect
Engraving: white
Density 4,6–4,7 g⋅cm − 3