Gemstone identifier by photo

The gemstone identifier compares photos of a rough, tumbled, polished or cut stone and suggests possible matches. Upload one to three photos of the same stone: the stone on white paper in daylight, a side view showing its shape, and a close view of the surface or inside. Then pick the form that fits best: rough crystal or pebble, tumbled or polished, faceted or set in jewelry, or not sure.

The result lists the gem materials that fit, the visible clues behind each and the lookalikes that remain. It also says what the photos could not settle. A follow-up question closes the result; answer it or ask your own. Where you found or bought the stone is the most useful note you can add.

Form comes first because it decides which clues are left to see. A rough crystal still has its natural faces, so its shape can point toward a group: ball-like garnets, barrel-shaped six-sided corundum, flat-topped six-sided beryl, striated tourmaline prisms or the double points of quartz. A water-worn pebble has lost those faces and shows only color, luster and what light does at a thin edge.

Tumbled stones, cabochons and beads are named mostly by pattern and luster. Agate, jasper, tiger’s eye, rose quartz, aventurine, sodalite and howlite each have a recognizable look. A cabochon, the smooth domed cut, is where most optical effects show best. Faceted stones give the least, because the cut hides crystal form. In jewelry, judge the stone, not the metal, stamp or tag.

For a rough crystal still attached to its rock, the crystal identifier compares its faces and shape.

Optical effects come next, because several are tied to one material. Rainbow patches that shift as you tilt the stone are play of color, found mainly in opal. A floating blue-white glow is adularescence, the sheen of moonstone. Broad blue, green or gold flashes across dark gray are labradorescence, seen in labradorite.

A single bright line across a domed stone is a cat’s-eye effect. Chrysoberyl, quartz and tourmaline can all show it, and a photo cannot separate them; golden-brown bands point toward tiger’s eye. A six-rayed star appears in star corundum and star garnet, another pair a photo cannot split. Tiny red-orange plates fit sunstone, green with small sparkles fits aventurine, and copper glitter in brown or blue is goldstone, a manufactured glass. Take two photos at slightly different tilts under one light to show any of these.

Next come transparency and what sits inside. Natural stones often hold small crystals, feathery cracks or cloudy patches. Round gas bubbles and curved swirls point toward glass or a synthetic stone instead. A large, perfectly clean stone with intense color can be natural, but it is also how many synthetics and glass look, so the gemstone identifier keeps those open.

Look straight down through the top facet of a cut stone. If the back facet edges look doubled, the stone is doubly refracting, like zircon, moissanite, peridot or tourmaline; diamond and glass are not. Color comes last, because one color spans many gems. Red can be garnet, ruby, spinel or tourmaline, and blue can be sapphire, aquamarine, topaz or tanzanite.

GIA notes that glass can be made in nearly any color and that plastic imitates amber, turquoise, jade and lapis in inexpensive jewelry. Plastic often feels warm and light for its size. The table pairs common clues with what they may point to.

Clear, shiny pebbles from a driveway, creek or beach are nearly always quartz, calcite, glass or a lost cubic zirconia. Quartz crystals with a point at each end are sold as Herkimer diamonds, but they are quartz. A rough diamond typically grows as an octahedron, shaped like two pyramids set base to base, often with curved faces and a greasy look.

The Arkansas Geological Survey describes diamonds found at Crater of Diamonds State Park as small and usually rounded, clean and slick, with an oily metallic luster. Visitors there may keep what they find; the other diamond-bearing bodies nearby are private land. The survey warns against striking a suspected diamond with a hammer, because diamonds cleave and break. Keep any candidate whole and show it to a gemologist.

For clear six-sided points, try the quartz identifier.

A photo cannot prove the species of a faceted stone. Expect two candidates that fit the color and look, with the note “cut stone, treatment unknown.” Diamond, ruby, sapphire and emerald always stay unverified, and so does any claim that a stone is natural, synthetic, heated, dyed, filled or irradiated. The gemstone identifier never gives carat weight, clarity grade, origin or value.

GIA lists heating, dyeing, fracture filling, impregnation, irradiation and coating among common treatments, and notes that many are not apparent to the unpracticed eye. GIA also states that sellers are legally required to disclose treatments. A qualified gemologist with instruments gives the final answer on species and treatment. Check any lab report with the lab that issued it.