Spotting Fake Labradorite: Essential Tests Every Buyer Must Know Before Purchase

Understanding Labradorite and Its Allure

Labradorite is a feldspar mineral renowned for its spectacular labradorescence—a schiller effect that flashes iridescent colors of blue, green, gold, and sometimes red or purple. This phenomenon occurs due to light interference within microscopic lamellar intergrowths of exsolved albite and orthoclase. The gem gemologically belongs to the plagioclase series, with a composition ranging from An_{50} to An_{70}. Its hardness of 6–6.5 on the Mohs scale and perfect cleavage make it both beautiful and delicate. For the discerning buyer, understanding these intrinsic properties is the first line of defense against imitations.

Why Fake Labradorite Floods the Market

The demand for affordable labradorite has spawned a thriving trade in fakes and treatments. Common imitations include synthetic spinel, colored glass, resin composites, and even assembled doublets. Some low-grade labradorite is heat-treated to enhance color, while others are coated with thin films to simulate a stronger flash. Buyers lured by bargain prices often receive stones that lack true labradorescence or are entirely artificial. Recognizing these deceptions requires a systematic approach combining visual examination, physical testing, and gemological instruments.

Visual Clues: The First Line of Defense

Begin with the naked eye under broad-spectrum daylight. Genuine labradorite displays a soft, wavy, or patchy schiller that moves as you tilt the stone. Fakes, especially glass or synthetic spinel, often show an overly uniform, sharp, or metallic flash that feels unnatural. Look for cleavage planes: real labradorite often has subtle planar cracks or cleavage surfaces that break light unpredictably. In contrast, glass simulants appear flawless and may exhibit rounded edges. Also note that natural labradorite’s color flash is usually confined to specific zones, not the entire surface. A stone that flashes bright colors from every angle is suspect.

Using a Loupe or Microscope: Magnification Reveals Truth

A 10x loupe or gemological microscope is essential. View the stone in reflected and transmitted light. Key features to identify include:
Cleavage and Inclusions: Natural labradorite often shows tiny stress fractures, silk-like needle inclusions, or fingerprint-like fluid inclusions. Glass imitations contain bubbles (spherical or elongated) and swirl lines from the mixing process. Synthetic spinel may exhibit curved striae (growth lines) and gas bubbles.
Schiller Layers: Under magnification, the labradorescence in natural stones originates from thin, subparallel exsolution lamellae. These appear as finely spaced, sometimes iridescent layers. Fake stones may have painted-on or applied coatings that look like paint flakes or uneven patches.
Double Refraction: Labradorite is birefringent, meaning you may see double images of inclusions or facet edges when viewed through a polariscope. Glass and amorphous synthetics are singly refractive and show no doubling. This test is simple and reliable.

The Polariscope Test: Isotropic vs Anisotropic

A polariscope distinguishes isotropic (singly refractive) from anisotropic (doubly refractive) materials. Labradorite is biaxial and anisotropic, so it will show four distinct bright-dark extinctions when rotated 360° between crossed polarizers. Glass, synthetic spinel, and resin are isotropic—they remain dark during rotation (unless strained, which can produce anomalous extinction but still not the classic four-sign pattern). This test quickly eliminates many fakes. Ensure the stone is clean and not too dark, as thick opaque pieces may be difficult to read.

Specific Gravity Testing: Weighing the Evidence

Labradorite has a specific gravity ranging from 2.68 to 2.71. Using a hydrostatic balance or heavy liquid sets (e.g., bromoform or methylene iodide diluted to correct density), you can measure this. Glass imitations typically have SG between 2.4–2.6, while synthetic spinel ranges from 3.58–3.61. Resin composites are even lighter (1.1–1.4). If the stone floats in a liquid of SG 2.70, it is likely labradorite; if it sinks rapidly, it may be spinel or other heavier material. This test requires careful setup and safety precautions with chemicals.

Spectroscopy and Advanced Testing

UV Fluorescence: A Telling Clue

While not definitive, UV fluorescence can help. Most natural labradorite shows weak to moderate whitish or greenish fluorescence under long-wave UV. Glass often fluoresces bright white, blue, or yellow depending on dopants. Some treated stones may show patchy fluorescence due to coatings. Always compare with a known reference sample.

Refractive Index (RI) Measurement

Using a refractometer, labradorite’s RI ranges from 1.554 to 1.573 (with a birefringence of ~0.010). Glass typically has a single RI between 1.50–1.70 (often around 1.52), but this overlaps with labradorite’s lower end. Synthetic spinel has a single RI of around 1.73, easily distinguishable. A common glass used for labradorite simulants has RI ~1.54, making it tricky. In such cases, birefringence reading is critical: if no shadow edge separation is observed, the material is isotropic and therefore not feldspar.

Thermal Conductivity and Toughness

Labradorite is a poor thermal conductor compared to glass. Place the stone against your cheek or lip—real stone feels cool to the touch and warms slowly. Glass warms quickly due to higher thermal diffusivity. However, this is subjective. More reliably, test cleavage: labradorite can be split along its perfect {001} and {010} cleavages using moderate pressure. Do not attempt this on finished jewelry, but if you have a loose rough sample, a deliberate strike may produce a broken plane. Glass fractures conchoidally, not along cleavage planes. Resin composites may chip or show plastic deformation.

Common Fake Treatments to Watch For

Market fakes are often labradorite rough that has been coated. A thin layer of titanium oxide or other dielectric materials can be deposited via sputtering or chemical vapor deposition to create intense iridescence. These coatings wear off quickly and are not permanent. Look for unnatural, rainbow colors that shift too dramatically or appear only on the surface. Under magnification, coatings may show scratches, peeling edges, or uneven color patches. Another trick: using low-quality labradorite and heating it to produce internal fractures that enhance flash, but this often leads to brittleness and risk of breakage. Such stones may have heat-altered inclusions or stress cracks radiating from tiny imperfections.

Practical Tips for Buyers

• Always ask for a return policy and buy from reputable dealers who provide disclosure of treatments.
• Request a gemological report from a lab like GIA, AGS, or IGI for high-value pieces.
• Learn to use a simple polariscope and 10x loupe—basic tools that save money in the long run.
• Join gemstone forums or local clubs to get hands-on experience with known genuine stones.
• Compare multiple stones side by side to develop an eye for natural schiller vs. artificial flash.

Conclusion

Fake labradorite is everywhere, but armed with knowledge of its gemological properties—RI, birefringence, specific gravity, cleavage, and inclusion characteristics—you can confidently separate the genuine from the imitation. By employing a combination of visual inspection, magnification, polarization, and density testing, you protect your investment and ensure the magic of labradorescence you see is the product of nature, not a manufactured illusion. Remember, if the deal seems too good to be true, it likely is. Vigilance and scientific testing are your best allies in the quest for authentic labradorite.