Quartz veins form when hot, silica-bearing fluids fill fractures in cracked rock, while pegmatites grow quartz from the last watery dregs of a melt.

Quartz is colourless in theory, yet iron, aluminium, natural radiation and microscopic inclusions create amethyst, citrine, rose and smoky varieties — here is how each forms.

Quartz, quartzite and glass look alike at arm's length, but hardness, streak, fracture and a simple double refraction trick separate them in minutes.