Diamond transparency, also called diaphaneity or pellucidity, is a physical property of a diamond that identifies the amount of light that can pass through the stone. The transparency level of diamonds varies among stones and may be classified as transparent, opaque or translucent. Transparency can be measured and evaluated by individuals and professionals alike using professional grading scales and charts.
As with other physical characteristics, the transparency of diamonds can change over time and is influenced by several external factors. The formation process of diamonds is one major factor that influences transparency. Diamonds form deep within the crust of the Earth's surface and often grow alongside other minerals and gems. Diamonds occur primarily in alluvial deposits and coexist with quartz, zircon, corundum and other minerals. Some diamonds form within minerals and, at times, minerals grow around diamonds, which affects their physical appearance.
Diamond color patterns range from clear to hazy and yellow; these stones may also appear as light brown, blue, black, green, red and pink. In addition to formation, other factors such as inclusions, shape and cut grade affect diamond transparency. Generally, diamonds that are most transparent are the shiniest and brightest, and these stones are considered top quality. Those that are hazy or cloudy in appearance, in contrast, are considered to be lower-grade gems.