A Gemstone Encyclopedia for Trade Buyers
By the Byrex Gems team, Toronto · Published 25 September 2026
A concise trade reference to fancy colour diamonds, ruby, sapphire, emerald, spinel, alexandrite, tourmaline, garnets, tanzanite and aquamarine: species, hardness, origins, treatments and value.
This reference covers the stones trade buyers meet most often at the fine end of the market. For each one we give the mineral species, hardness on the Mohs scale, key colours, main sources, common treatments, what laboratories typically report and the factors that drive value. The information is drawn from GIA's Gem Encyclopedia and research, and from the published standards of GRS, SSEF, Gübelin and the Laboratory Manual Harmonisation Committee (LMHC).
Summary table
Fancy colour diamond
Species: Diamond (carbon)
Mohs: 10
Key origins: Australia (Argyle, closed 2020), southern Africa, Russia, Brazil
Common treatment: Irradiation, HPHT, coating (must be disclosed)
Ruby
Species: Corundum
Mohs: 9
Key origins: Myanmar, Mozambique, Vietnam, Thailand–Cambodia, East Africa, Madagascar
Common treatment: Heating; lead-glass filling in lower grades
Sapphire
Species: Corundum
Mohs: 9
Key origins: Kashmir, Myanmar, Sri Lanka, Madagascar, Australia, Thailand, Montana
Common treatment: Heating; beryllium diffusion
Emerald
Species: Beryl
Mohs: 7.5–8
Key origins: Colombia, Zambia, Brazil, Pakistan, Afghanistan
Common treatment: Oil, wax or resin in fissures
Spinel
Species: Spinel
Mohs: 8
Key origins: Myanmar, Sri Lanka, Vietnam, Tajikistan, Tanzania
Common treatment: Rarely treated
Alexandrite
Species: Chrysoberyl
Mohs: 8.5
Key origins: Russia (historic), Brazil, Sri Lanka, East Africa
Common treatment: Rarely treated
Tourmaline (incl. Paraíba)
Species: Tourmaline
Mohs: 7–7.5
Key origins: Brazil, Nigeria, Mozambique, Afghanistan, Pakistan
Common treatment: Heating, irradiation
Garnets (tsavorite, demantoid, spessartine)
Species: Garnet group
Mohs: 6.5–7.5
Key origins: Kenya, Tanzania, Madagascar, Namibia, Russia
Common treatment: Rarely treated
Tanzanite
Species: Zoisite
Mohs: 6–7
Key origins: Merelani, Tanzania only
Common treatment: Heating (nearly universal)
Aquamarine and beryl
Species: Beryl
Mohs: 7.5–8
Key origins: Brazil, Pakistan, Nigeria, Madagascar, Mozambique
Common treatment: Heating
Diamond: fancy colours
Species and hardness: carbon; 10 on the Mohs scale. Colours and causes: GIA estimates that only about one carat in 10,000 of polished diamond shows fancy colour. Nitrogen causes yellow and boron causes blue. Natural radiation produces green. Pink, red, purple and brown are linked to plastic deformation of the crystal lattice (GIA; G&G, Winter 2018). Sources: the Argyle mine in Western Australia dominated modern pink supply until it closed in November 2020, producing more than 90% of the world's pink diamonds, according to Rio Tinto (Rio Tinto). GIA's research lists other pink diamond sources in Russia, southern Africa and Brazil, and historically India. Treatments: irradiation, HPHT processing and coatings can create or alter colour. What labs report: GIA gives a colour grade (hue, tone and saturation, with descriptors from Faint to Fancy Vivid, Fancy Deep and Fancy Dark), the origin of colour (natural or treated) and, on some reports, diamond type. Value factors: hue and strength of colour come first. Fancy Intense and Fancy Vivid generally command higher prices, and red, pink, blue and green are the rarest (GIA).
Ruby
Species and hardness: red corundum; 9. Colour: chromium causes both the red and a red fluorescence that can intensify colour in daylight. Iron-rich rubies from basalt-related deposits show less of this glow (GIA). Sources: the Mogok area of Myanmar has been renowned for more than five centuries. Mozambique's Montepuez deposits are a major modern source. Vietnam, the Thailand–Cambodia border, Afghanistan, Tajikistan, Pakistan, Sri Lanka, Kenya, Tanzania and Madagascar also produce ruby (GIA). Treatments: most rubies are heated. Lower grades may be glass-filled, diffused or dyed (GIA 4Cs). What labs report: heated or unheated, any residues (for example GRS codes H(a) to H(d)), origin, and at some labs a trade colour term such as pigeon's blood. Value factors: a pure, vivid red that is not too dark, then clarity, cut and size. Fine rubies over one carat are rare.
Sapphire, including padparadscha and fancy colours
Species and hardness: corundum in every colour except red; 9. Colours: blue (coloured by iron and titanium; SSEF), plus pink, yellow, orange, violet, green, colour-change and parti-coloured stones. Sources: Kashmir, where sapphires were found around 1881 and the richest production came in the few years that followed. Other sources are Myanmar, Sri Lanka, Madagascar, Australia, Thailand, Cambodia and Montana (GIA). Treatments: heating is widespread and accepted. Sri Lankan "geuda" is heated to develop blue. Beryllium diffusion became a major issue around 2001, first in padparadscha-like colours (G&G). Padparadscha: the LMHC defines it as a subtle mixture of pinkish orange to orangey pink with pastel tones and low to medium saturation, from any origin. Diffusion and other artificial colouring disqualify a stone, and it must pass a colour stability test (LMHC). What labs report: heating, diffusion, origin, and terms such as royal blue or cornflower where a lab uses them. Value factors: saturated, even colour and good transparency. Kashmir commands the highest origin premium, with Myanmar, Sri Lanka and Madagascar also producing top gems (GIA).
Emerald
Species and hardness: green to bluish green beryl; 7.5–8, with inclusions (the "jardin") that make it less tough than its hardness suggests (GIA). Colour: chromium, vanadium or both. Sources: in Colombia, Muzo is known for darker pure greens, Chivor for lighter, slightly bluish greens and Coscuez for slightly yellowish greens. Brazil (Minas Gerais), Zambia, Pakistan and Afghanistan are also important (GIA). Treatments: filling fissures with oil, wax or resin is the most common. Dyeing is used on low-grade material. What labs report: degree of clarity enhancement, using LMHC F1–F3 (minor to significant) or a lab's own scale, sometimes the filler type, and origin. GRS adds an "Old Mine/Muzo Green" appendix for qualifying colours. Value factors: vivid bluish green to pure green colour, then the level of enhancement. Untreated fine emeralds command higher prices (GIA 4Cs).
Spinel
Species and hardness: magnesium aluminium oxide (MgAl2O4); 8. Colours: chromium gives red and pink, iron gives violet to blue, and cobalt gives vivid blue (GIA). The Black Prince's Ruby in Britain's Imperial State Crown is a red spinel. Sources: Mogok (Myanmar), Sri Lanka, Luc Yen (Vietnam), Tajikistan, Tanzania and Pakistan (GIA). A 52 kg crystal found near Mahenge, Tanzania, in 2007 opened a notable new source of vivid pinkish red spinel (SSEF). Treatments: spinel is rarely treated. Heated stones can be detected with photoluminescence. What labs report: natural or synthetic, heating, origin (GIA offers origin for red spinel), and "cobalt spinel" where cobalt dominates the colour under LMHC rules (LMHC). Value factors: vivid red and cobalt blue are the most valued. Fine stones above five carats are uncommon (GIA).
Alexandrite and chrysoberyl
Species and hardness: chrysoberyl (BeAl2O4); 8.5. Colour: alexandrite is the chromium-bearing, colour-change variety, green to bluish green in daylight and red to purplish red in incandescent light. Under LMHC rules, other colour-change stones must be described by their own species name (LMHC). Chrysoberyl also produces cat's-eye stones. Sources: first found in Russia's Urals around 1830. Today's sources are Brazil, Sri Lanka and East Africa (GIA). Treatments: rarely treated. Laboratory-grown alexandrite and imitations exist, and GIA warns that an inexpensive stone with a strong red-green change is probably one of them. What labs report: natural or synthetic, the strength of the colour change and origin. Value factors: the strength and purity of the colour change above all. Most cut stones are under one carat, and fine stones over five carats are especially costly (GIA).
Tourmaline, including Paraíba-type
Species and hardness: tourmaline; 7–7.5. Colours: almost every colour, including rubellite (red), indicolite (blue), bicoloured watermelon tourmaline and copper-bearing Paraíba (GIA). Sources: Brazil (especially Minas Gerais), Afghanistan, Pakistan, Kenya, Madagascar, Mozambique and the United States. Electric blue and green copper-bearing tourmaline appeared in Brazil's Paraíba State in the late 1980s, and similar material was found in Mozambique and Nigeria in the early 2000s (GIA). Treatments: heating and irradiation. Irradiated colours can fade with heat or strong light. What labs report: under LMHC rules, "Paraíba tourmaline" means a blue to green tourmaline coloured mainly by copper and manganese, from any locality (LMHC). GIA also offers origin opinions for Paraíba-type tourmaline. Value factors: bright, pure colour. GIA notes that fine stones with laboratory-documented Paraíba origin command a premium (GIA).
Tsavorite and other garnets
Species and hardness: the garnet group has six main species (pyrope, almandine, spessartine, grossular, andradite and uvarovite), with hardness from 6.5 to 7.5 (GIA). Key varieties: tsavorite is a vivid green grossular, mostly from Kenya, Tanzania and Madagascar. Demantoid is green andradite with very high dispersion, known from Russia and now Namibia. Its "horsetail" inclusions are prized but also occur in stones from Iran and Italy. Spessartine gives the orange "mandarin" garnets of Namibia and Tanzania (GIA; GIA buyers guide). Treatments: garnets are rarely treated. What labs report: species and variety, and natural or synthetic. Value factors: colour and size. Tsavorite and demantoid rise sharply in price per carat as size increases.
Tanzanite
Species and hardness: blue to violet zoisite; 6–7, so it needs care in rings. Colour: coloured by vanadium and strongly pleochroic, showing blue, violet and purple in different directions. Source: only the Merelani Hills of northern Tanzania, where it was discovered in 1967 (GIA). Treatments: heating is nearly universal. The LMHC notes that in some cases heating cannot currently be determined, and that a stone qualifies as tanzanite only if blue or purple clearly dominates (LMHC). Value factors: deep, saturated blue-violet. Colour strength generally improves with size.
Aquamarine and other beryls
Species and hardness: beryl; 7.5–8. Colour: iron produces blue to greenish blue. Other beryl varieties include morganite (pink) and heliodor (golden yellow) (GIA). Sources: Minas Gerais in Brazil has been important for two centuries. Pakistan, Kenya, Madagascar, Nigeria, Zambia, Mozambique and the United States also produce aquamarine (GIA). Treatments: heating to remove yellowish tones is common. What labs report: species and variety, and treatment where detectable. Value factors: a stronger, purer blue is preferred. Most cut stones are eye-clean, so colour and cutting drive price.
Using this reference
Treatments, colour terms and origin opinions differ between laboratories, as our guides to laboratory reports explain. Always read the exact wording on a report, and check it with the issuing laboratory's online verification service.
For advice on any of these stones, or to ask about stones with laboratory reports, email info@byrex.com or send a WhatsApp message to +1 (437) 450-3786.