Rubies

Rubies shine red against black rocks. Ruby, the common name for the mineral corundum in its red form, is a precious gemstone. If the mineral has a blue color it's known as a sapphire. Made up of the elements aluminum and oxygen, corundum also can be yellow, gray, or brown.

Topaz

This cut topaz gemstone shows off its striking blue coloration, but the mineral also occurs in a colorless form or with a yellow or green color. A red topaz is a rarity. Topaz occurs in the igneous rock rhyolite.

Quality Control

Rubies shine red against black rocks. Ruby, the common name for the mineral corundum in its red form, is a precious gemstone. If the mineral has a blue color it's known as a sapphire. Made up of the elements aluminum and oxygen, corundum also can be yellow, gray, or brown.