Identification

The global gemstone market is filled with imitation, synthetic, and treated stones — many of which are sold without proper disclosure. For a buyer without gemological training, distinguishing a genuine natural gemstone from a convincing substitute can seem impossible. But there are practical tests and observations that any buyer can make, without laboratory equipment, that significantly reduce the risk of being deceived.

This guide covers the most useful tests for common gemstones — particularly rubies, sapphires, and emeralds, which are the most frequently imitated. It also explains the difference between the three main categories of "non-genuine" gems: imitations, synthetics, and treated stones.

Know Your Enemy: Three Types of Non-Genuine Gems

Imitation stones are materials that look like a gemstone but have a completely different chemical composition. Glass, plastic, and cubic zirconia (CZ) are common imitations for diamond and sapphire. They are not chemically related to the gem they imitate and are usually significantly less expensive to produce.

Synthetic stones are chemically, physically, and optically identical to natural gemstones — but they are created in a laboratory rather than formed in the earth. Synthetic ruby, synthetic sapphire, and synthetic emerald are all real gemstones in a chemical sense, but they lack the geological history, rarity, and therefore the value of natural stones. The key problem is that synthetics are sometimes sold as natural without disclosure.

Treated stones are natural gemstones that have been artificially enhanced to improve colour or clarity. Heat treatment, beryllium diffusion, fracture filling, and surface coating are common treatments. Many treatments are industry-accepted and disclosed; others are not. An unheated natural ruby is worth dramatically more than an equivalent heat-treated stone.

Test 1: The Temperature Test

Real gemstones — particularly sapphire, ruby, and diamond — are excellent conductors of heat. When you hold a genuine gemstone briefly against your cheek or lip (which are sensitive to temperature), it feels cool and takes a moment to warm up. Glass and plastic imitations warm up almost immediately to body temperature. This test is not definitive, but it immediately separates glass and plastic from genuine corundum and diamond.

Test 2: Look for Bubbles Under Magnification

Glass imitations almost always contain gas bubbles trapped during the manufacturing process. Use a 10× loupe (a small magnifying glass available cheaply from jewellery supply stores) to examine the interior of any suspect stone. Round or elongated bubbles are a definitive sign of glass. Natural gemstones contain inclusions — crystals, needles, fingerprints, feathers — but not round gas bubbles. Synthetic stones made by the flame fusion process (the most common method for synthetic ruby and sapphire) show curved growth lines called "curved striae" — another sign of synthetic origin visible under magnification.

Test 3: Check the Hardness

Sapphire and ruby (corundum) have a Mohs hardness of 9 — they will scratch glass easily (glass is hardness 5–6) and will not be scratched by a steel file (hardness 6–7). If you have a loose stone of unknown identity, you can carefully attempt to scratch a piece of glass with the stone's culet (the pointed bottom). A genuine sapphire or ruby will leave a mark; glass, cubic zirconia, and synthetic spinel will not scratch glass as readily. Use this test only on loose stones and only on the culet — never on the facets of a set stone.

Test 4: Check for Doubling of Back Facets

Many natural gemstones — ruby, sapphire, emerald, tourmaline, peridot — are doubly refractive, meaning light splits into two rays as it passes through the stone. When you look through the top of a doubly refractive stone with a loupe, the back facet edges appear doubled. Glass and cubic zirconia are singly refractive and show no doubling. This is one of the most reliable home tests. Simply hold the stone between your eye and a light source and look straight down through the table facet — if the back edges appear as double lines, the stone is doubly refractive and almost certainly not glass or CZ.

Test 5: UV Fluorescence

A simple UV torch (available cheaply online) can reveal important information. Natural rubies from Burma (Myanmar) typically show a strong red fluorescence under longwave UV. Ceylon rubies show a weaker fluorescence. Red garnets — a common ruby imitation — show no fluorescence. Natural blue sapphires are typically inert (no fluorescence) under UV. If someone is selling you a "natural sapphire" that glows strongly orange or yellow under UV, be cautious — this can indicate synthetic or treated material.

The One Test That Beats All Others

All of the above tests are useful preliminary screenings, but none of them replaces laboratory testing. A refractometer reading, specific gravity measurement, and spectroscopic analysis by a qualified gemologist can conclusively identify any gemstone in minutes. For any purchase above USD 300–500, the cost of a professional identification report is small relative to the value of the stone and the risk of buying something other than what you were told.

The most important protection any gem buyer has is a certificate from a reputable laboratory. Buy the certificate as much as you buy the stone.

Disclaimer: Home tests provide preliminary guidance only and are not a substitute for professional gemological assessment.