Chrysoberyl is an oxide of iron and aluminum, discovered in 1790 by a German geologist who named this new stone Krisoberil or "golden beryl".
Chrysoberyl forms in pegmatites, i.e. magmatic rocks. Current mines are located in Algeria, Brazil and the United States.
The two most famous types of chrysoberyls are :
The alexandrite: which is a very rare variety of chrysoberyl with the singularity of having a "change color" effect. In daylight the stone is green-blue and in incandescent light it appears red-pink. It was discovered in 1842 by Nils Gustaf who dedicated his discovery to Tsar Alexander II, green and red being the colors of the tsars.
The main deposits were in Russia, but are now exhausted. Today, Brazil has several mines but the stones are of lesser quality and not all change color.
Cat's eye is a shimmering variety of chrysoberyl. In cold light a white line appears that moves across the width of the stone depending on the orientation of the light.
This effect is due to inclusions, channels inside the stone.
Cat's eye chrysoberyls are always cut in cabochon, which emphasizes the movement of the line.