Learn Gemmology
FGA curriculum-aligned content covering crystallography, physical and optical properties, inclusions, treatments, and synthetics. 138 articles across 8 categories.
Start here
Recommended foundations to read first- 1
Crystal Systems
The seven crystal systems and their characteristic symmetry elements.
- 2
Physical Properties
Hardness, specific gravity, cleavage, fracture, and lustre.
- 3
Optical Properties
Refractive index, birefringence, pleochroism, dispersion, and other optical properties of gemstones.
- 4
Gemstone Treatments
Heat treatment, filling, diffusion, coating, and detection methods for treated gemstones – with per-species diagnostic depth.
Fundamentals
9 topics covering crystal systems, advanced crystallography, and twin laws in gemmology, plus 6 more
Crystal Systems
The seven crystal systems and their characteristic symmetry elements.
beginnerPhysical Properties
Hardness, specific gravity, cleavage, fracture, and lustre.
beginnerChemical Properties
Gem chemistry, chromophores and colour causes, allochromatic vs idiochromatic minerals, charge transfer, and colour centres.
intermediateOptical Properties
Refractive index, birefringence, pleochroism, dispersion, and other optical properties of gemstones.
intermediateAdvanced Crystallography
Twinning, Miller indices, crystal habits, crystal forms, point groups, and crystal growth mechanisms.
advancedTwin Laws in Gemmology
Named twin laws – spinel, Carlsbad, Manebach, Baveno, albite, pericline, Brazil, Dauphiné, Japan – and corundum parting, with diagnostic applications.
advancedColour Theory in Gemmology
The physics and chemistry of gem colour: crystal field theory, charge transfer, colour centres, allochromatic and idiochromatic minerals, and band-gap colouration.
advancedAdvanced Optical Properties
Interference figures, optic sign determination, complete absorption spectra, luminescence, and anomalous double refraction.
advancedOptic Sign Determination
Determining positive or negative optic sign for uniaxial and biaxial gems using the refractometer, lambda plate, and interference figures.
advancedEquipment
13 topics covering gem testing equipment overview, the refractometer, and the polariscope, plus 10 more
Gem Testing Equipment Overview
Introduction to gemmological instruments, testing workflow, and which tool to use for different identification tasks.
beginnerThe Refractometer
Refractive index measurement using the gemmological refractometer, including faceted and cabochon techniques, birefringence reading, and troubleshooting.
beginnerThe Polariscope
Using the polariscope to determine optic character (isotropic vs anisotropic), detect anomalous double refraction, and observe interference figures.
beginnerThe Dichroscope
Using the dichroscope to observe pleochroism in coloured gemstones, distinguishing dichroic from trichroic materials.
beginnerThe UV Lamp
Using ultraviolet light for fluorescence testing, distinguishing LWUV from SWUV reactions, and safety considerations.
beginnerOther Testing Tools
Chelsea filter, thermal conductivity probes, specific gravity measurement, and other supporting gemmological instruments.
beginnerChelsea Colour Filter
Using the Chelsea Colour Filter as a chromium discriminator for gem identification – including the species reaction table, lighting requirements, and diagnostic limitations.
beginnerSpecific Gravity Measurement
Hydrostatic weighing and heavy-liquid methods for measuring specific gravity – the density-based property used to identify and confirm gem species.
beginnerThe Spectroscope
Using the spectroscope to observe absorption spectra, identifying characteristic patterns for gem species and detecting treatments.
intermediateThe Microscope
Using the gemmological microscope for inclusion study, illumination techniques, and immersion methods to identify gems and detect treatments.
intermediateDiamond Screening Instruments
Thermal conductivity probes, electrical conductivity testers, DiamondView, DiamondSure, and reflectance meters – the tools used to screen loose diamonds and detect synthetic and simulant materials.
intermediateConoscopic Observation and Interference Figures
Using convergent polarised light to observe interference figures that reveal a gemstone's optic character (uniaxial or biaxial) and optic sign – an advanced polariscope technique.
advancedAdvanced Laboratory Instruments
Diploma-level awareness of FTIR, UV-Vis-NIR, Raman, EDXRF, LA-ICP-MS, and photoluminescence spectroscopy – what each detects and its key gemmological applications.
advancedSpecies
20 topics covering corundum, beryl, and garnet group, plus 17 more
Quartz
Quartz species including amethyst, citrine, rose quartz, smoky quartz, rock crystal, and chalcedony varieties with properties and identification.
beginnerOlivine (Peridot)
Olivine species and its gem variety peridot with properties, characteristic inclusions, sources, and identification.
beginnerPearl
Pearl formation, types (natural, Akoya, South Sea, Tahitian, freshwater), grading factors, identification, and care.
beginnerCoral
Precious coral species including red (ox blood), pink (angel skin), and related varieties with identification, treatments, and conservation.
beginnerAmber
Amber fossilised tree resin including Baltic, Dominican, and Burmese varieties with inclusions, identification, and distinguishing from copal.
beginnerJet
Jet fossilised wood including Whitby jet, properties, Victorian significance, identification, and distinguishing from simulants.
beginnerCorundum
Corundum species including ruby and sapphire varieties, properties, inclusions, origins, treatments, and historical significance.
intermediateBeryl
Beryl species including emerald, aquamarine, morganite, heliodor, goshenite, and red beryl with properties, inclusions, and treatments.
intermediateGarnet Group
The garnet group minerals including almandine, pyrope, spessartine, grossular, andradite, and their gem varieties like demantoid and tsavorite.
intermediateTourmaline Group
The tourmaline group including elbaite varieties (rubellite, indicolite, Paraíba), dravite, and chrome tourmaline with properties and identification.
intermediateSpinel
Spinel species including red, blue, pink, and colour-change varieties with properties, origins, historical significance, and identification.
intermediateTopaz
Topaz species including imperial, blue, sherry, and colourless varieties with properties, treatments, and identification.
intermediateFeldspar Group
Feldspar group gems including moonstone, labradorite, sunstone, amazonite, and orthoclase with properties, phenomena, and identification.
intermediateChrysoberyl
Chrysoberyl species including alexandrite and cat's eye chrysoberyl (cymophane) with properties, colour change, chatoyancy, and identification.
intermediateZircon
Zircon species including blue, colourless, and fancy colours with metamict types, properties, treatments, and identification.
intermediateZoisite
Zoisite species including tanzanite, thulite, and anyolite with properties, colour change, treatments, and identification.
intermediateDiamond
Diamond type classification, the 4Cs grading system, fancy colours, natural vs lab-grown identification, and diamond verification instruments.
intermediatePyroxene Group
Pyroxene group gems including jadeite, spodumene (kunzite, hiddenite), and diopside (chrome diopside) with properties and identification.
intermediateAmphibole Group (Nephrite)
Amphibole group gems, primarily nephrite jade, with properties, comparison to jadeite, sources, and identification.
intermediateOpal
Opal species including precious opal (black, white, crystal, boulder, fire) and common opal with play of colour, patterns, and identification.
intermediateIdentification
15 topics covering beryllium diffusion – deep diagnostic reference, inclusions overview, and lead glass-filled ruby – deep diagnostic reference, plus 12 more
Gemstone Treatments
Heat treatment, filling, diffusion, coating, and detection methods for treated gemstones – with per-species diagnostic depth.
intermediateComposite Stones
Doublets, triplets, assembled stones, and their detection including opal doublets, garnet-topped doublets, and soudé emeralds.
intermediateBeryllium Diffusion – Deep Diagnostic Reference
Full per-method detection protocol for beryllium lattice diffusion in corundum, with disclosure standards and stability data.
advancedLead Glass-Filled Ruby – Deep Diagnostic Reference
Full detection protocol for composite (lead glass-filled) ruby, with nomenclature, durability, and disclosure standards.
advancedHPHT Diamond Treatment – Deep Diagnostic Reference
Full detection protocol for HPHT-treated natural diamonds, including type-by-type outcomes, DiamondView patterns, and photoluminescence signatures.
advancedCVD Diamond Detection – Deep Diagnostic Reference
Full detection protocol for CVD synthetic diamonds, distinguishing from natural and HPHT-treated stones using DiamondView, FTIR, and photoluminescence.
advancedSynthetic Gemstones
Synthetic gem production methods including flame fusion, hydrothermal, flux growth, and detection techniques.
advancedInclusions
(8 topics)Inclusions Overview
Introduction to inclusions, their classification, and microscopy techniques for examination.
intermediateSolid Inclusions
Crystal inclusions - identifying mineral guests trapped within gemstones during formation.
intermediateFluid Inclusions
Two-phase, three-phase, and negative crystal inclusions - trapped fluids that reveal formation conditions.
intermediateGrowth Features
Colour zoning, growth tubes, twinning, phantoms, and other patterns formed during crystallization.
intermediateFeathers & Fingerprints
Healed fractures, fingerprint inclusions, and liquid feathers - characteristic healing patterns in gems.
intermediateSilk & Needle Inclusions
Rutile silk, needle inclusions, and their role in asterism and origin determination.
intermediateNatural vs Synthetic Indicators
Distinguishing natural gemstones from synthetics using inclusion evidence.
intermediateSurface Features
Naturals, bearding, etch channels, and other surface-related inclusion features.
intermediatePhenomena
16 topics covering optical phenomena overview, asterism (star effect), and chatoyancy (cat's eye effect), plus 13 more
Optical Phenomena Overview
Introduction to optical phenomena in gemstones including light interaction principles and summary of major phenomena.
intermediateAsterism (Star Effect)
Asterism in gemstones including star ruby, star sapphire, and other star stones with formation, quality factors, and identification.
intermediateChatoyancy (Cat's Eye Effect)
Chatoyancy in gemstones including chrysoberyl cat's eye, the milk and honey effect, and other chatoyant gems.
intermediateAdularescence
Adularescence in moonstone including cause, types of moonstone, quality factors, and distinction from labradorescence.
intermediateLabradorescence
Labradorescence in labradorite and spectrolite including cause, colour range, quality factors, and distinction from adularescence.
intermediatePlay of Colour
Play of colour in precious opal including cause, pattern types, body tones, and quality assessment.
intermediateColour Change
Colour change phenomenon in gemstones including alexandrite, colour-change garnet, sapphire, and diaspore with causes and grading.
intermediateAventurescence
Aventurescence in gemstones including sunstone and aventurine quartz with causes, types, and quality factors.
intermediateIridescence
Iridescence in gemstones including fire agate, ammolite, iris quartz, and surface coatings with causes and identification.
intermediateSchiller and Peristerescence
Schiller and peristerescence in feldspar – the mechanism of non-spectral lamellar scattering, named species, and distinction from adularescence, labradorescence, aventurescence, and chatoyancy.
intermediateSilk Effect
The silk effect in Kashmir sapphire and Burmese ruby – velvety appearance from rutile-needle clouds, mechanism, distinction from asterism, and diagnostic significance for origin and heat-treatment detection.
intermediateFluorescence and Phosphorescence
Fluorescence and phosphorescence in gemstones – Stokes shift mechanism, LWUV vs SWUV regimes, species reaction table, phosphorescence afterglow, and diagnostic applications for natural vs synthetic identification.
intermediateFire and Dispersion
Fire in faceted gemstones – dispersion as differential refraction by wavelength, the B–G interval, named dispersion values, relationship to facet design, and distinction from diffraction-based spectral effects.
intermediatePearl Orient
Pearl orient – the soft iridescent surface bloom of fine nacre, arising from thin-film diffraction and interference at aragonite tablet layers, distinguished from body colour, lustre, and fluorescence.
intermediateTenebrescence
Tenebrescence – reversible photochromic colour change in hackmanite driven by S₂⁻ radical colour centres, mechanism, named species, and diagnostic distinction from the alexandrite effect and irradiation-induced colour changes.
advancedAlexandrite Effect – Physical Mechanism
Deep dive into the alexandrite effect – Cr³⁺ in trigonal crystal field, the dual transmission window, photopic peak balance, named species including garnets, sapphire, and synthetic spinel, and how to test colour change under standardised illuminants.
advancedOrigin
60 topics covering origin determination overview, afghanistan – gem origins overview, and australian gems - overview, plus 57 more
Iran – Nishapur (Neyshabur) Turquoise
Persian turquoise from Neyshabur, Khorasan – the global colour standard; volcanic tuff host, spider-web matrix, Cu-Al phosphate, treatment assessment.
intermediateOrigin Determination Overview
Introduction to geographic origin determination for gemstones including methodology, premium factors, and laboratory reports.
advancedKashmir Sapphire
Kashmir sapphire characteristics, diagnostic inclusions, velvety appearance, historical significance, and market premiums.
advancedSri Lankan (Ceylon) Gems
Sri Lankan sapphire, padparadscha, spinel, and other gems with characteristics, inclusions, and historical significance.
advancedColombian Emerald
Colombian emerald from Muzo, Chivor, and Coscuez with three-phase inclusions, characteristics, and market position.
advancedColombian Emerald Mines – Sub-Distinctions
Mine-level diagnostics for Muzo (parisite + halite), Chivor (pyrite dominant), Coscuez, La Pita, and trapiche emerald; cross-reference to colombia.yaml.
advancedZambian Emerald
Zambian emerald characteristics, inclusions, comparison with Colombian, and market position.
advancedBrazil – Imperial Topaz and Emerald Sub-distinctions
Ouro Preto imperial topaz (Cr-coloured, strong LWUV fluorescence); Itabira vs Carnaíba emerald distinction (Cr vs V dominant, inclusion differences). Cross-reference brazil/ folder.
advancedCambodia – Pailin Sapphire and Battambang Ruby
Cambodian gem deposits from Pailin (basaltic sapphire and ruby) and Battambang (marble-hosted ruby); Khmer Rouge era hiatus; distinction from Thai material.
advancedVietnam – Luc Yen Ruby and Cobalt-Blue Spinel
Marble-hosted ruby and spinel from Luc Yen (Yen Bai) and Quy Chau; low-Fe high-Cr chemistry, cobalt-blue spinel, distinction from Burmese material.
advancedTajikistan – Kuh-i-Lal Spinel (Balas Ruby)
Kuh-i-Lal Gorno-Badakhshan red and pink spinel – historic "Balas ruby" of the Persian courts; Cr-coloured marble-hosted; trace element distinction from Mogok and Luc Yen.
advancedIndia – Alexandrite, Diamond (Panna), and Garnet
Indian gem deposits – Andhra Pradesh alexandrite and chrysoberyl, Panna kimberlite diamond, Orissa garnet; geological context; Koh-i-Noor attribution qualified.
advancedMozambique – Montepuez Ruby and Paraíba Tourmaline
Montepuez ruby (Cabo Delgado) – two-type amphibolite-hosted and alluvial; Mavuco Paraíba-type Cu-bearing tourmaline; LA-ICP-MS origin discrimination.
advancedZimbabwe – Sandawana Emerald and Marange Diamond
Sandawana (Belingwe) emerald – vivid Cr-rich, tremolite inclusions, very small; Marange alluvial diamond; Murehwa chrysoberyl [CITATION NEEDED].
advancedEthiopia – Wollo Opal and Shakiso Emerald
Wollo (Welo) hydrophane opal – volcanic host, water-absorbing, distinct from Australian; Shakiso mica-schist emerald; Tigray sapphire [CITATION NEEDED].
advancedAfghanistan
(3 topics)Afghanistan – Gem Origins Overview
Hindu Kush gem province – lapis lazuli (Sar-e-Sang), Panjshir emerald, Nuristan kunzite; multiple geological settings; conflict and artisanal mining context.
advancedLapis Lazuli – Sar-e-Sang, Afghanistan
Sar-e-Sang (Badakhshan) lapis lazuli – the canonical ancient-world source, >7,000 years of continuous mining, geochemical fingerprinting, grades and quality.
intermediatePanjshir Emerald – Afghanistan
Hydrothermal-sediment hosted Panjshir emerald; high Fe UV-Vis bands, low Li, three-phase inclusions in black shale context; distinction from Colombian.
advancedAustralia
(6 topics)Australian Gems - Overview
Introduction to Australia's gem production, world leadership in opal, and significant sapphire and chrysoprase deposits.
advancedLightning Ridge Black Opal
The world's most valuable opal from Lightning Ridge, NSW - body tone, patterns, and quality factors.
advancedQueensland Boulder Opal
Australian boulder opal with ironstone matrix backing - sources, patterns, and assessment criteria.
advancedWhite Opal & Crystal Opal
Coober Pedy white opal and Australian crystal opal varieties - characteristics, quality grades, and market position.
advancedAustralian Sapphire
Australian sapphire characteristics including parti-sapphires, dark blues, and comparison with Asian sources.
advancedArgyle Diamonds
The historic Argyle mine - world's primary pink diamond source, closure in 2020, and impact on the diamond market.
advancedBrazil
(5 topics)Brazilian Gems - Overview
Introduction to Brazil's diverse gem production including Paraíba tourmaline, imperial topaz, aquamarine, and other varieties.
advancedParaíba Tourmaline
Brazil's legendary copper-bearing tourmaline - discovery, neon colours, and its position as the most valuable tourmaline.
advancedBrazilian Emerald
Brazilian emerald characteristics, comparison with Colombian material, and market position.
advancedBrazilian Aquamarine & Topaz
World-renowned Brazilian aquamarine including Santa Maria quality, and exclusive imperial topaz from Ouro Preto.
advancedBrazilian Tourmaline
Brazilian tourmaline varieties beyond Paraíba - rubellite, indicolite, chrome tourmaline, and other colours.
advancedBurma
(5 topics)Burmese Gems - Overview
Introduction to Myanmar's legendary gem production from Mogok and other regions, including ethical considerations.
advancedBurmese Ruby
Mogok and Mong Hsu ruby - the pigeon blood standard, diagnostic inclusions, and comparison with other sources.
advancedBurmese Sapphire
Mogok sapphire characteristics, inclusions, and market position relative to Kashmir and Ceylon.
advancedBurmese Spinel
Mogok spinel - historic confusion with ruby, exceptional red and pink colours, and growing collector interest.
advancedBurmese Jadeite
Imperial jade from Myanmar's Kachin State - the world's finest jadeite, characteristics, and the Asian market.
advancedEast Africa
(6 topics)East African Gems - Overview
Introduction to East Africa's emergence as a major coloured gem region, covering Tanzania, Kenya, and Mozambique.
advancedTanzanite
Tanzania's signature gemstone from the Merelani Hills - single-source rarity, colour grades, and heat treatment.
advancedTsavorite Garnet
East Africa's finest green garnet from Kenya and Tanzania - discovery, characteristics, and comparison with emerald.
advancedEast African Ruby
Ruby from Mozambique (Montepuez) and Kenya (John Saul Mine) - characteristics, inclusions, and market significance.
advancedMahenge Spinel
Tanzania's exceptional neon pink to red spinel from the Mahenge region - discovery, characteristics, and market impact.
advancedParaiba-Type Tourmaline
Mozambican copper-bearing tourmaline with neon blue-green colours - discovery, characteristics, and the origin terminology debate.
advancedMadagascar
(5 topics)Madagascar Gems - Overview
Introduction to Madagascar's emergence as a major gem source and its diverse production of sapphire, ruby, and rare species.
advancedMadagascar Sapphire
Ilakaka sapphire region - characteristics, Ceylon comparison, diagnostic inclusions, and quality assessment.
advancedMadagascar Ruby
Ruby from Andilamena and other regions - characteristics, heat treatment, beryllium diffusion concerns.
advancedMadagascar Beryl
Aquamarine, morganite, and limited emerald production from Madagascar - characteristics and market position.
advancedRare Madagascar Gems
Grandidierite, demantoid garnet, tourmaline, and other rare species from Madagascar's diverse geology.
advancedPakistan
(4 topics)Pakistan – Gem Origins Overview
Himalayan collision zone gem deposits – Swat emerald, Hunza ruby, Katlang topaz, Skardu aquamarine; multiple geological settings.
advancedSwat Valley Emerald – Pakistan
Ophiolite-hosted Cr-rich emerald from Mingora, Swat Valley; three-phase fluid inclusions, chromian muscovite, low Li chemistry, talc-carbonate paragenesis.
advancedHunza Ruby – Pakistan
Marble-hosted ruby from Hunza/Gilgit-Baltistan; low-Fe high-Cr chemistry analogous to Mogok; marble-suite inclusions; strong LWUV fluorescence.
advancedKatlang Pink Topaz – Pakistan
Chromium-coloured pink to champagne topaz from Katlang, Mardan district; Cr³⁺ colouring diagnostic, calcite-vein hosted, rare among topaz globally.
advancedRussia
(4 topics)Russia – Ural Gem Deposits Overview
Ural Mountains gem belt – demantoid garnet, alexandrite, emerald; Yakutia diamond; serpentinite and mica-schist geological settings.
advancedRussian Demantoid Garnet – Ural Mountains
Ural demantoid (andradite, Cr-coloured); horsetail inclusions – byssolite terminology and Kissin 2021 mineralogical correction; LA-ICP-MS origin discrimination from Namibia and Madagascar.
advancedRussian Alexandrite – Tokovaya District, Ural Mountains
Tokovaya district alexandrite – 1830 discovery, named for Tsar Alexander II; benchmark colour change; mica-schist host; market position vs synthetic.
advancedUral Emerald – Malyshevsky, Russia
Ural emerald from the Malyshevsky/Izumrudnye Kopi deposit; phlogopite mica inclusions diagnostic; Cr+V chromophores; mica-schist contact zone genesis.
advancedThailand
(4 topics)Thailand – Gem Origins Overview
Southeast Asian gem province centred on Chanthaburi, Trat, Kanchanaburi, Bo Phloi, and Bo Rai; world leader in corundum heat treatment and trading.
advancedThai Ruby – Chanthaburi-Trat and Bo Rai Types
Basaltic-hosted Siam ruby from Chanthaburi-Trat and Bo Rai; diagnostic high-Fe chemistry, 451/460/470 nm iron triplet, weak fluorescence, alluvial habit.
advancedThai Sapphire – Bo Phloi and Kanchanaburi Types
Basaltic high-Fe blue sapphire from Bo Phloi and Kanchanaburi; strong 450/460/470 nm iron triplet, common heat treatment, basalt-suite inclusions.
advancedThai Blue Zircon – Heat-Treatment Hub
Thailand as the global centre for heat-treating Cambodian and Vietnamese zircon rough into blue zircon; origin, treatment process, and identification.
intermediateUsa
(3 topics)USA – Gem Origins Overview
US gem deposits – Montana sapphire, Utah red beryl, Arizona peridot, California and Maine tourmaline; geologically diverse patchwork provinces.
intermediateMontana Sapphire – Yogo Gulch, Rock Creek, Missouri River
Yogo Gulch steely-blue lamprophyre sapphire (no heat needed), Rock Creek and Missouri River alluvial pastels; distinct Fe/Ti/Mg trace element chemistry; US commercial significance.
advancedUtah Red Beryl – Wah Wah Mountains
World's only commercial red beryl source – Mn³⁺-coloured beryl in Eocene topaz rhyolite, Wah Wah Mountains, Utah; properties, inclusions, market rarity.
advancedMarket
4 topics covering laboratory reports, treatment disclosure & ethics, and grading and valuation, plus 1 more
Grading and Valuation
Colour grading (hue, tone, saturation), clarity assessment, cut quality, carat weight, and value factors for coloured gemstones.
intermediateLaboratory Reports
Understanding gem laboratory reports from GIA, Gübelin, SSEF, GRS, and other major labs with terminology, grading, and certification.
advancedTreatment Disclosure & Ethics
Treatment disclosure requirements, ethical standards, trade practices, and consumer protection in the gemstone industry.
advancedProfessional Practice
Report writing, disclosure requirements, legal aspects, professional ethics, and laboratory certification for gemmologists.
advancedCare
Learn about gem care and durability
FGA Curriculum Alignment
This content is aligned with the Gem-A (Gemmological Association of Great Britain) FGA diploma curriculum. While comprehensive, this resource is not a substitute for formal gemmological education and hands-on training with reference stones.