International School of Gemology Education Series: The Story of Apatite

Reading Time: 7 minutes With the ongoing economic pressures on the jewelry industry to utilize more affordable gemstones, Apatite has taken front stage for many jewelry designers and manufacturers. This relatively unknown gemstone provides the three main ingredients for creating a successful gemstone market: beauty, durability, and availability. Apatite, derived from the Greek word “apatein” meaning “to deceive,” was named due to its historical confusion with other minerals like beryl and tourmaline, which it often resembles. Despite its relative softness compared to many other gemstones, apatite is gaining popularity for its vibrant colors and unique optical properties. Formation: Apatite is a phosphate mineral that forms in a variety of geological environments. It is a common accessory mineral found in:

• Igneous Rocks: It crystallizes from magma and lava, appearing in granites, pegmatites, and volcanic rocks. Gem-quality apatite often forms in pegmatites.
• Metamorphic Rocks: It can also be found in metamorphic rocks like marble, schist, and gneiss, formed under intense heat and pressure.
• Hydrothermal Veins: It can also form from hot, mineral-rich fluids circulating through cracks in existing rocks.

Apatite crystals form in the hexagonal crystal system (as shown here) and are excellent for student spectroscope study due to the unique spectrum. The ISG has yellow apatite crystals available for student purchase. Contact the ISG office for more details. Sources: Apatite is found globally, with notable gem-quality deposits in several countries:

• Brazil: Known for producing significant quantities of fine-quality blue, green, and yellow apatite.
• Madagascar: A major source of vibrant blue-green (“Paraiba-like”) apatite, as well as yellow and green varieties.
• Myanmar (Burma): Produces attractive blue and green crystals.
• Mexico: Known for producing yellow and green apatite.
• Canada: Some deposits yield blue and green crystals.
• United States: Found in various localities, though generally not in commercial quantities for gem use.

Quality Factors: The value of apatite is primarily determined by the following factors:

• Color: This is the most important factor. Apatite comes in a wide spectrum of colors, including blue, green, yellow, pink, purple, colorless, and even cat’s-eye varieties.
• Blue: Often the most sought-after, especially the neon blue-green reminiscent of Paraiba tourmaline.
• Green: Can range from yellowish-green to a rich emerald-like green.
• Yellow: Often bright and attractive.
• Pink and Purple: Rarer and highly desirable.
• Clarity: Apatite is a Type II gemstone, meaning it often has some inclusions visible to the naked eye. Eye-clean or nearly eye-clean stones command higher prices. However, certain inclusions can create desirable effects like:
• Cat’s-Eye Effect (Chatoyancy): Caused by parallel needle-like inclusions, creating a band of light that moves across the surface of a cabochon-cut stone. These are highly prized.
• Cut: Due to its relative softness (5 on the Mohs scale), apatite is often cut into cabochons to minimize scratching and chipping. However, well-cut faceted stones with good brilliance and symmetry are highly valued. Shapes include ovals, rounds, cushions, and emerald cuts.
• Carat Weight: Larger, high-quality apatite gemstones are rarer and thus more valuable.

Identification Methods: While difficult to distinguish from other gems without gemological tools, here are some characteristics and tests a gemologist might use:

• Color: Apatite is famous for its neon blue color. It mimics a fine quality Paraiba Tourmaline (the real thing from Brazil) but yet has its own unique aura of blue that is unlike any other gemstone.
• Spectroscope: Viewed through a diffraction grating spectroscope, apatite shows a distinct absorption line in the yellow that greatly helps make a diagnostic identification.

• Refractive Index (RI): Apatite has a distinct refractive index range (typically 1.632 to 1.638, with a birefringence of 0.002 to 0.008), which can be measured with a refractometer.
• Specific Gravity (SG): Its specific gravity (ranging from 3.16 to 3.22) can help differentiate it from similar-looking gems.
• Pleochroism: Many apatite specimens exhibit pleochroism, meaning they show different colors when viewed from different angles. This is particularly noticeable in strong colors like blue and green.

Values: The value of apatite can vary significantly based on the quality factors discussed above:

• Entry-Level: Smaller, less intensely colored, or more included stones can be quite affordable, as low as a few dollars per carat for commercial quality.
• Mid-Range: Good quality, eye-clean stones in attractive colors (especially blue and green) can fetch $20 to $100 per carat, depending on size and intensity of color.
• High-End: Premium pieces, such as large, eye-clean, neon blue or rare pink/purple apatite, especially those with exceptional color saturation, can reach several hundred dollars per carat, sometimes even exceeding $500 per carat for truly exceptional specimens or fine cat’s-eye material.
• Cat’s-Eye Apatite: These command a premium, with prices depending on the sharpness of the eye and the overall quality of the stone.

Despite its relative softness, apatite is a beautiful and increasingly popular gemstone for collectors and those seeking unique and vibrant jewelry pieces. Its diverse colors and relatively accessible price point make it an attractive option in the world of colored gemstones. Visit the ISG website to learn more about our world-class programs in gemology and jewelry appraisal at our low tuition rates.