The Light of Chatoyancy——Chrysoberyl
The word Apatite comes from Greek, meaning “deception,” because the mineral’s appearance can resemble that of emerald, sapphire, aquamarine, or amethyst, leading to confusion.
Apatite refers to a group of calcium phosphate minerals that contain either chlorine (Cl) or fluorine (F). The most common species is fluorapatite, followed by chlorapatite and hydroxylapatite. Apatite often contains rare earth elements like cerium (Ce), uranium (U), and thorium (Th), which can impart a wide range of colors, including colorless, yellow, blue, purple, green, brown, and white. Some apatite specimens exhibit phosphorescence, meaning they continue to glow after exposure to UV light. Additionally, apatite has strong pleochroism, where the color changes when viewed from different angles. However, due to its lower hardness, apatite is not as widely sought after in the jewelry market.
Apatite is found in igneous, metamorphic, and sedimentary rocks. In igneous rocks, apatite occurs mainly in pegmatites or hydrothermal veins, with gemstone-quality apatite typically sourced from pegmatitic granite. In sedimentary rocks, apatite forms through exogenic processes and contributes to the creation of phosphorite, a rock rich in phosphate minerals. In metamorphic rocks, apatite is generally found as an accessory mineral. Gem-quality apatite is most often extracted from alluvial deposits.
Commercial Value of Apatite
Apatite is easily confused with several common gemstones due to its appearance. Though it may be difficult to distinguish them with the naked eye, gemologists can easily identify apatite by examining its refractive index, birefringence, specific gravity, and clarity. However, it should be noted that apatite and tourmaline have similar refractive indices, requiring birefringence for differentiation. In the case of cabochon-cut stones, rather than faceted gems, distinguishing between the two becomes more challenging.
Industrially
About 90% of the phosphorus in nature comes from apatite, making apatite an important industrial mineral for extracting phosphorus. This element is widely used in various fields such as medical products, chemical products, textiles, clothing, inorganic products, and the removal of toxic substances. Its applications are quite extensive.
Ornamentally
Gem-quality cat’s eye apatite often contains parallel fibrous or tubular inclusions that easily create a chatoyancy effect in cabochon cuts. When selecting cat’s eye apatite, opt for visually flawless stones and vibrant colors like vivid blue-green (rainbow blue), which resembles Paraiba tourmaline, or intense green and royal blue. If these colors are combined with the cat’s eye effect, they are even more valuable and desirable.
Brownish-yellow cat’s eye apatite closely resembles the coveted cat’s eye chrysoberyl, and it is common to find apatite varieties with a similar “honey color,” which is highly sought after in chrysoberyl.
Though apatite lacks pronounced cleavage, making it relatively impact-resistant, its low hardness means it still requires careful handling to prevent scratching. Additionally, apatite is sensitive to acids, so it should not be exposed to acidic liquids or soaked in hot springs, as this could lead to potential dissolution.
