Updated: Jul 26, 2021
Aventurine is a variety of translucent quartz or quartzite with abundant small plate- or flake-shaped inclusions. Light entering the quartz strikes these inclusions and reflects from them. This produces a sparkly appearance known as "aventurescence." The inclusions can also impart a distinct, and often beautiful, color to the material.
When the inclusions are abundant and in a common orientation, their reflections can be eye-catching. This property, along with desirable colors, are what give aventurine its appeal as a gemstone. Aventurine is most often green, but also occurs in orange, yellow, red, pink, brown, white, gray, and blue. - Learn more at Geology.com