Lapis Lazuli is a deep-blue metamorphic rock cherished for its intense color for thousands of years. It is a composite material, not a single mineral, primarily containing the blue mineral Lazurite, alongside components like Calcite and Pyrite. Historically, it was used in jewelry, carvings, and ground into the prized pigment ultramarine, adorning works like the funeral mask of Tutankhamun. Learning to identify the characteristics of genuine Lapis Lazuli ensures you acquire an authentic piece.
Evaluating Color and Mineral Inclusions
The signature deep, royal blue color of Lapis Lazuli comes from the mineral Lazurite, which typically makes up 25% to 40% of the rock’s composition. Highly valued specimens display a uniform, intense blue hue, though the color can range from violetish blue to greenish blue. However, a perfectly uniform and vivid color can sometimes indicate a dye treatment rather than natural quality.
Genuine Lapis Lazuli is characterized by two primary inclusions. The first is Pyrite, which appears as brass-colored, metallic flecks scattered throughout the blue matrix. These inclusions should look like naturally embedded mineral particles, resembling a “stardust” effect. While high-grade material may have sparse, finely distributed Pyrite, its complete absence can suggest a fake.
The second common inclusion is Calcite, visible as white or grayish patches and streaks. Excessive Calcite significantly lowers the stone’s quality, giving it a mottled or pale appearance by diluting the deep blue Lazurite. In high-quality Lapis Lazuli, the Calcite veining is minimal or nearly invisible, allowing the intense blue to dominate.
Analyzing Physical Properties
Simple physical tests can help confirm the mineral nature of Lapis Lazuli. The stone is relatively soft, ranking between 5 and 5.5 on the Mohs scale of hardness. This means it can be scratched by a steel nail or glass, but not easily by a fingernail or a copper penny.
Lapis Lazuli has a specific gravity, or density, ranging from 2.7 to 2.9. This density means a genuine piece should feel heavier than common imitations like plastic or glass of the same size. A noticeable weight difference is a quick indicator of an imitation.
The streak test involves rubbing the stone against unglazed porcelain. Authentic Lapis Lazuli will consistently leave a pale blue streak, characteristic of its mineral composition. This test helps distinguish it from dyed or synthetic materials that might leave a different color or no streak.
Distinguishing Lapis Lazuli From Imitations
Distinguishing imitations often relies on close inspection and simple chemical tests. A common treatment is dyeing low-grade Lapis Lazuli or materials like Jasper, Howlite, or Magnesite to achieve a vivid blue color. To check for dye, gently rub an inconspicuous area with a cotton swab dipped in acetone or alcohol. If the color transfers, the stone has been dyed.
Sodalite is a natural mineral frequently mistaken for Lapis Lazuli due to its similar blue color. Sodalite is typically a duller or grayer blue, and the major distinguishing factor is Pyrite. Genuine Sodalite usually lacks the characteristic golden Pyrite flecks. While Sodalite may contain white Calcite, it often appears as clearly defined veins rather than the subtly blended effect seen in Lapis Lazuli.
Synthetic versions, sometimes called Gilson Lapis, attempt to replicate the natural stone. The Pyrite inclusions in these synthetics often appear too uniform, perfectly scattered, or overly shiny, lacking the irregular nature of natural grains. High-quality synthetic imitations often lack the white Calcite veining present in nearly all natural Lapis Lazuli. Glass and plastic imitations feel warm to the touch, while genuine Lapis Lazuli remains cool.