Gemstone identifier: what makes a stone valuable
Colour, clarity, cut, and crystal system — the properties that gemologists and collectors use to evaluate and identify faceted and rough gemstones.
The gemological approach to identification
Professional gemologists identify stones using optical and physical properties measured with specialised instruments — refractometers, spectroscopes, and polariscopes — but a working knowledge of the underlying properties enables useful field assessments. Refractive index, which describes how much a stone bends light, is species-specific and a primary identifier. Crystal system determines cleavage and optical behaviour: cubic minerals (diamond, garnet, spinel) are singly refractive, while non-cubic minerals (sapphire, tourmaline, topaz) are doubly refractive, splitting light into two rays. Specific gravity — the stone's density relative to water — distinguishes stones of similar appearance: diamond (3.52) is much denser than quartz (2.65), which is why a diamond feels heavier than a similar-sized piece of clear quartz. RockLens uses visual characteristics as a fast first filter for rough stones; faceted stones require the additional instrumental tests that a gemologist performs.
Reading inclusions and growth features
Inclusions — solid, liquid, or gas trapped inside a stone during formation — are forensic evidence of a mineral's geological history and are essential tools for both identification and provenance. Rutile needles in sapphire and ruby create the star effect (asterism) when cut en cabochon; the same needles at different concentrations are diagnostic for natural versus synthetic stones. Emeralds are famous for their jardin (garden) — a dense network of inclusions characteristic of the hydrothermal conditions in which they formed, very different from the clean appearance of synthetic emerald grown in a laboratory. Colour zoning (bands of different saturation) and growth planes visible under magnification indicate natural formation. Gemological microscopy at 10–40× magnification reveals these features; RockLens's close-up photo analysis can identify gross inclusion types and colour distribution as an initial assessment for rough and larger faceted specimens.
Common gemstone families and their collector significance
The corundum family (ruby and sapphire) dominates the fine gemstone market because of its hardness (9 on the Mohs scale), wide colour range from red through every colour of sapphire, and durability. Origin matters enormously: Burmese pigeon-blood ruby and Kashmir sapphire command premiums far above equivalent stones from other localities. The beryl family encompasses emerald (green), aquamarine (blue-green), morganite (pink), heliodor (yellow), and goshenite (colourless) — chemically identical but coloured by different trace elements. The tourmaline group offers the broadest colour spectrum of any single mineral species, from achroite (colourless) through rubellite (red), indicolite (blue), and Paraíba tourmaline (neon blue-green), with Paraíba stones commanding the highest per-carat prices of any tourmaline due to their copper colouration. Understanding family relationships helps collectors interpret value: stones in the same mineral family share physical durability properties even when their colours create different market positions.
FAQ
How can I tell if a gemstone is natural or synthetic?
Natural and synthetic gemstones share the same chemical composition and physical properties, making separation difficult by eye alone. The most reliable indicators are inclusion types: natural stones contain inclusions formed by geological processes (mineral crystals, fluid inclusions, growth planes) while synthetics grown by flame fusion show curved growth striae, and those grown hydrothermally show characteristic chevron-pattern inclusions. Lab-grown diamonds show no inclusions of the type found in naturals but may show metallic flux inclusions (from HPHT growth) or cloud-like striations (from CVD growth). Gemological testing with a UV lamp, microscope, and spectroscope provides definitive evidence.
What is a cabochon cut and why is it used for certain stones?
A cabochon is a smooth, domed cut without facets, polished to a convex top and flat or slightly concave base. It is used for opaque or translucent stones where faceting would not add brilliance, and for stones with optical phenomena that are best displayed with a smooth surface: star sapphires and rubies display asterism only when cut en cabochon, because the dome creates the correct geometry for the reflected star. Cat's-eye chrysoberyl and moonstone's adularescence similarly require the curved surface to reveal their optical effects.
Does RockLens work for identifying rough (uncut) gemstones?
RockLens performs best on rough specimens and polished but unfaceted mineral surfaces. The app analyses crystal form, natural lustre, colour distribution, and surface texture — features that are clearly visible in raw material. Faceted stones are harder to identify visually because the faceting obscures the natural crystal form, and many gem species look similar once they are cut and polished. For rough minerals, a clean fresh surface photographed in natural light gives the most accurate result.