GIA is a trusted authority known for its rigorous, objective analysis of both natural and cultured pearls. Learn about how ...

Figure 1. Pleochroism in a 15 ct tanzanite, as seen with the unaided eye through the crown and the pavilion sides and ends. Photo by Wimon Manorotkul. In describing colored gemstones, the major ...

Gem-quality diaspore occupies an important position in the gem market due to its rarity, striking pleochroism, and color-change phenomenon (figure 1). The material’s value depends on these factors. A ...

Opal can range from 5 to 6.5 on the Mohs hardness scale. Hardness and toughness Gem and mineral hardness is measured on the Mohs scale. The numbers are based on the relative ease or difficulty with ...

The Ponderosa mine is now producing commercial quantities of the gem-quality labradorite feldspar known as sunstone. This gem material exhibits unique optical and physical properties that include a ...

This chart focuses primarily on the types of natural inclusions found in tourmaline, as well as the minerals in which tourmaline can be found as an inclusion. Treatments such as enhancement of ...