Apatite is a calcium phosphate mineral known for its vast and varied color range, which frequently causes confusion with other precious stones. German geologist Abraham Gottlob Werner named the mineral in 1786, choosing the moniker from the Greek word apatao, meaning “to deceive” or “to cheat.” This name was chosen because apatite specimens often closely resemble minerals such as peridot, beryl, and tourmaline, making visual identification difficult. Apatite is transparent to translucent and boasts a spectrum that makes it one of the most chromatographically diverse minerals found in nature.
The Spectrum of Apatite Colors
The most sought-after colors in the gem trade are vibrant blues and blue-greens, which can rival the electric glow of the rare Paraíba tourmaline. This highly prized, neon blue apatite is often the result of heat treatment on naturally green stones. Green is arguably the most common color, with shades ranging from pale pastel to rich, emerald-like green. Historically, a bluish-green variety was sometimes called moroxite, and other green specimens have been nicknamed “asparagus stone.”
Apatite also occurs in yellow shades, ranging from soft lemon to deep golden hues. These yellow varieties sometimes exhibit a purplish-pink fluorescence under ultraviolet light. Violet, purple, and pink varieties are rarer but highly valued, adding to the mineral’s diversity. The mineral can also be found in brown, gray, and completely colorless forms.
The Mineralogical Source of Color
The wide range of color in apatite is a direct consequence of trace elements substituting into the mineral’s crystal structure. In its purest state, the calcium phosphate mineral would be entirely colorless. Coloration arises when small amounts of foreign ions replace the calcium atoms within the hexagonal crystal lattice.
Manganese is responsible for generating the less common pink and purple hues. Iron is a common trace element that often imparts the prevalent greenish tones seen in many apatite crystals. The brilliant blue and intense blue-green shades are often attributed to the inclusion of rare earth elements or sometimes to iron, especially after heat treatment. Color can also be created by crystal defects known as color centers. These centers are imperfections that trap electrons, which then absorb and transmit light at different wavelengths, resulting in a visible color.
Apatite’s Place in Mineralogy
Apatite is a name for a group of closely related phosphate minerals that share a similar chemical structure and physical properties. The three primary members are fluoroapatite, chloroapatite, and hydroxylapatite, named for the fluorine, chlorine, or hydroxyl ions that define their composition. The general chemical formula is based on calcium phosphate, which is geologically significant as it is the same mineral component found in the bones and teeth of vertebrates, including humans.
The mineral is the defining specimen for the value of five on the Mohs scale of hardness. This relatively low hardness makes apatite susceptible to scratches and chipping, meaning it is better suited for collector pieces than for daily-wear jewelry. Despite this fragility, apatite is industrially significant because it is a primary source of phosphorus, mined extensively for the production of agricultural fertilizers.