Topaz
Topaz is allochromatic, which means that its colour is caused by impurity elements or defects in its crystal structure rather than by an element of its basic chemical composition. The element chromium causes natural pink, red, and violet-to-purple colours in topaz. Imperfections at the atomic level in topaz crystal structure can cause yellow, brown, and blue colour. Brown is a common topaz colour, and the gem is sometimes mistakenly called “smoky quartz.”
