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

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 ...

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 ...

Figure 1. Diamonds such as this 1.15 ct round brilliant are some of the most highly sought-after gem materials and may contain inclusions that give the gemologist clues about their origin or treatment ...

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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 ...

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 ...

Figure 1. This emerald contains a brown crystal of the rare mineral parisite. There is also an oil-filled cavity showing a blue and orange flash effect, along with two large trapped gas bubbles. This ...

With the increasing use of radiation to color enhance gemstones, the issue of radioactivity has become a source of concern for gemologists worldwide. This article examines the basic characteristics of ...

Irradiated South Sea cultured pearls (SSCPs) from the Pinctada maxima mollusk typically show colors from light gray to silver. It is difficult to identify gamma-ray irradiation of SSCPs using standard ...

Figure 1. The vivid colors seen in fine gem-quality spinel are derived from the mixing between multiple different chromophores in a range of ratios and concentrations, as in this fine 13.52 ct ...

Figure 1. These 20 completely non-nacreous pen pearls, from the group of 22 samples in this study, are set against a pen shell displaying both nacreous (left) and non-nacreous areas (right). Photo by ...