Gem Identification

The first step in gem identification is careful visual observation: Color: Note the hue (red, blue, green, etc.), tone (light to dark), and saturation (intensity). Some gems have characteristic colors that are strong identifiers. Clarity: Observe inclusions, fractures, and other internal features. These can be diagnostic - for example, rutile needles in sapphire or "horsetail" inclusions in demantoid garnet. Luster: How light reflects from the surface. Can be metallic, adamantine (diamond-like), vitreous (glass-like), silky, pearly, or dull. Transparency: Whether the gem is transparent, translucent, or opaque. This affects how light passes through and can indicate certain gem types. Crystal Habit: The shape the crystal naturally forms. While cut gems may not show this, uncut specimens reveal characteristic forms. Phenomena: Special optical effects like asterism (star effect), chatoyancy (cat's eye), play-of-color (opal), or color change (alexandrite).

Measuring physical properties provides definitive identification: Hardness (Mohs Scale): Resistance to scratching. Diamond (10) scratches everything; talc (1) is scratched by everything. Hardness testing requires care to avoid damaging the gem. Specific Gravity: Density relative to water. Measured using hydrostatic weighing or heavy liquids. Each gem has a characteristic range. For example, diamond (3.52), corundum (4.00), and topaz (3.53) have distinct values. Refractive Index: How much light bends when entering the gem. Measured with a refractometer. Single values for isotropic gems (like diamond), or two values for anisotropic gems (like sapphire). Birefringence: The difference between the two refractive indices in anisotropic gems. High birefringence (like zircon, 0.059) creates visible doubling of facet edges. Dispersion: The separation of white light into colors (fire). Diamond has high dispersion (0.044), creating its characteristic sparkle. Pleochroism: Different colors seen from different directions. Strong pleochroism (like in tanzanite) is diagnostic.

Professional gemologists use sophisticated equipment: Spectroscopy: Analyzing how gems absorb light at different wavelengths. Each gem has a characteristic spectrum that acts like a fingerprint. UV Fluorescence: Many gems fluoresce under ultraviolet light. Ruby typically fluoresces red, while some diamonds fluoresce blue. This is a useful identification tool. Polariscope: Determines if a gem is single-refractive (isotropic) or double-refractive (anisotropic). Essential for identifying simulants. Microscopy: High-magnification examination reveals inclusions, growth patterns, and other features that identify gems and detect treatments or synthetics. X-ray Diffraction: For difficult cases, X-ray analysis can definitively identify crystal structure. Chemical Analysis: EDX (Energy Dispersive X-ray) or other methods determine elemental composition, crucial for identifying some gems.

Key identification features of popular gems: Diamond: Hardness 10, RI 2.42, SG 3.52, high dispersion, often fluoresces blue. May show natural inclusions or growth features. Ruby/Sapphire (Corundum): Hardness 9, RI 1.76-1.77, SG 4.00, strong pleochroism. Rutile needles create silk; color zoning is common. Emerald (Beryl): Hardness 7.5-8, RI 1.57-1.58, SG 2.72. Characteristic inclusions (three-phase inclusions, jardin) are diagnostic. Topaz: Hardness 8, RI 1.61-1.64, SG 3.53, strong pleochroism. Can be confused with citrine or sapphire but has distinct properties. Tourmaline: Hardness 7-7.5, RI 1.62-1.64, SG 3.06, very strong pleochroism. Often shows color zoning and characteristic inclusions. Quartz Varieties: Amethyst, citrine, ametrine all have RI 1.54-1.55, SG 2.65. Identified by color and sometimes by twinning patterns.

Identifying treatments and synthetics is crucial: Heat Treatment: Many gems are heated to improve color or clarity. This is permanent and often undetectable without advanced testing. Common in sapphire, ruby, tanzanite, and topaz. Irradiation: Exposing gems to radiation changes color. Some treatments are stable, others fade. Blue topaz is often irradiated. Fracture Filling: Filling surface-reaching fractures with glass or resin improves appearance. Common in emerald and ruby. Visible under magnification. Coating: Thin films applied to surfaces to change color. Can wear off over time. Check for surface scratches or uneven color. Synthetic Gems: Lab-created gems have the same chemical and physical properties as natural gems. Identification requires examining inclusions, growth patterns, and sometimes advanced testing. Simulants: Materials that look like gems but have different properties. Cubic zirconia, moissanite, and glass are common simulants. Physical testing easily distinguishes them.