NOBILITH Academy

Glossary

Gemmology terms explained briefly and clearly – the reference section of the NOBILITH Academy.

Absorption spectrum: When light passes through a gemstone, the stone absorbs certain wavelengths – the rest make up its colour.
Afghanistan: Afghanistan is an old source of ruby and emerald; both are mined in the mountains of the Hindu Kush.
Asterism: Asterism is the star effect of certain gemstones: on a domed stone a four- or six-rayed star appears and glides across the surface as the stone moves.
Australia: Australia was home to the Argyle mine, the most important source of pink and red diamonds.
Beryl: Beryl is the mineral species to which emerald and aquamarine belong.
Birefringence: Many gemstones split a ray of light into two rays travelling at slightly different speeds.
Botswana: Botswana is among the world’s most important diamond producers by value.
Brazil: Brazil is the type locality of Paraíba tourmaline and an important source of emerald, alexandrite and diamond.
Cabochon: A cabochon is a smoothly domed stone without facets.
Canada: Since the late 1990s Canada has mined diamonds in the Northwest Territories.
Carat: The carat is the unit of weight for gemstones: 1 carat equals 0.2 grams and is divided into 100 points.
Chrysoberyl: Chrysoberyl is the mineral species of alexandrite and cat’s eye.
Clarity: Clarity describes a stone’s inclusions and surface features.
Clarity enhancement (F1–F3): Fissures in emeralds and other stones are often filled with oil or resin to make them less visible.
Clarity type (I, II, III): Because each gem species grows differently, GIA assigns coloured gemstones to three clarity types.
Colombia: Colombia is the classic source of emerald; its stones have set the standard for centuries.
Colour change: Some gemstones show a different colour depending on the light source.
Colour distribution: Colour distribution describes whether a coloured diamond’s colour appears even or uneven when viewed face-up.
Colour origin: Colour origin states whether a coloured diamond’s colour formed naturally or through a treatment such as irradiation or HPHT.
Colour zoning: Colour zoning means that colour is not evenly distributed in a stone but appears in bands, patches or zones.
Cornflower Blue: «Cornflower Blue» describes sapphires with a pure, highly saturated blue in medium tone – velvety and luminous at once.
Corundum: Corundum is the mineral species of ruby and sapphire – crystallised aluminium oxide with a hardness of 9, the hardest natural gem material after diamond.
Cutting style: Cutting style describes how the facets are arranged.
Diamond clarity scale (FL to I3): Diamonds are assessed under 10× magnification on a fixed scale: FL (flawless), IF (internally flawless), VVS1–VVS2 (very, very slightly included), VS1–VS2 (very slightly), SI1–SI2 (slightly) and I1–I3 (inclusions visible to the eye).
Diamond colour scale (D to Z): Colourless diamonds are graded on a scale from D (completely colourless) to Z (noticeably yellowish or brownish).
Diffusion: In diffusion, elements such as beryllium or titanium are introduced into the stone from outside under great heat to alter or create its colour.
Dispersion: Dispersion is a stone’s ability to split white light into spectral colours – the coloured flashes known as «fire».
Enhancement: In the trade «enhancement» is often used as a softer word for treatment – for example heating sapphires or oiling emeralds.
Ethiopia: Within a few years Ethiopia has become a new source of emerald, sapphire and Paraíba tourmaline.
Extinction: Extinction refers to dark areas in a cut stone where little light returns.
Eye clean: Eye clean means that no inclusions are visible to the unaided eye at a normal viewing distance.
Fancy grade: For coloured diamonds the fancy grade describes the interplay of tone and saturation in nine levels: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Intense, Fancy Vivid, Fancy Deep and Fancy Dark.
Fluorescence: Fluorescence is a stone’s glow under ultraviolet light.
Fracture filling: In fracture filling, fissures reaching the surface are filled with oil, resin or glass to make them less visible.
Heating with residues (TE1–TE5): When ruby and sapphire are heated, additives can melt and close fissures, leaving glassy residues.
HPHT treatment: HPHT stands for «high pressure, high temperature».
Hue: Hue is the colour the eye actually perceives – red, blue, green or a transition between them.
Inclusion: Inclusions are natural features inside a stone: tiny crystals, fluids, needles or healed fissures.
India (Golconda): For around two thousand years India was the only known source of diamonds.
Irradiation: In irradiation, diamonds and some coloured stones gain a new colour through high-energy radiation, often followed by heating.
Kashmir: Kashmir sapphires are considered the epitome of velvety blue – although the deposit was productive for only a few years.
Laboratory report: A laboratory report is the examination document of an independent gemmological laboratory.
Lead-glass filling: Heavily fractured rubies may have their fissures filled with lead-bearing glass.
LMHC: The Laboratory Manual Harmonisation Committee (LMHC) is an association of leading gemmological laboratories.
Loupe clean: Loupe clean means that no inclusions are visible even under a 10× loupe.
Lustre: Lustre describes how a stone’s surface reflects light.
Madagascar: Since the 1990s Madagascar has been one of the most important sources of sapphire – and it also yields ruby, emerald and alexandrite.
Montana (USA): Montana is the most important sapphire source in the United States.
Mozambique: Since 2009 Mozambique has been the world’s most productive ruby source and one of the homes of Paraíba tourmaline.
Muzo Green: «Muzo Green» describes emeralds with a vivid, warm, slightly yellowish green associated with the legendary Muzo mine in Colombia.
Myanmar (Burma): Myanmar, formerly Burma, has for centuries been regarded as the most important source of fine rubies.
Nigeria: In 2001 Nigeria became the first source of Paraíba tourmaline outside Brazil.
No indications of heating (NTE): «No indications of heating» – often abbreviated NTE on reports – means the laboratory found no evidence of heat treatment in a ruby or sapphire.
Origin opinion: How laboratories determine a gemstone’s origin – and where the limits lie.
Origins of gemstones: Where NOBILITH gemstones occur – the best-known origins for each gemstone at a glance.
Padparadscha: Padparadscha is a sapphire variety with a delicate blend of pink and orange – from pinkish orange to orangey pink, with pastel tones and low to medium saturation.
Paraíba: Paraíba denotes tourmalines whose luminous neon to electric blue or green is caused by copper.
Pigeon Blood: «Pigeon Blood» is the highest colour designation for rubies: a saturated, luminous red with strong red fluorescence that gives the stone an inner glow.
Pleochroism: Pleochroism means that a stone shows different colours from different viewing directions – for example a sapphire that looks blue from above and greenish blue from the side.
Refractive index: The refractive index states how strongly a stone bends and slows light.
Royal Blue: «Royal Blue» describes sapphires with a deep, saturated blue that often carries a hint of violet and stays rich even in dimmer light.
Russia (Urals): Emerald and alexandrite were discovered in the Urals – today Russia is important above all for diamonds.
Saturation: Saturation describes the purity and strength of a colour.
Secondary hue: A secondary hue is a second colour visible alongside the dominant one.
Silk: Silk refers to fine, needle-like inclusions, usually rutile, forming a delicate network in ruby and sapphire.
South Africa: With the finds from 1867 onwards, South Africa made diamonds available in larger quantities for the first time.
Species and variety: Laboratories first name the mineral species and then the variety.
Sri Lanka (Ceylon): Sri Lanka is one of the world’s oldest gem sources; sapphires have been mined here for more than two thousand years.
Synthetic: A synthetic stone is made in a laboratory and has the same chemical composition and structure as its natural counterpart – so it is not an imitation, but neither is it a product of nature.
Tanzania: Tanzania offers an extraordinary variety: sapphire, ruby, alexandrite and even pink diamonds.
Thailand and Cambodia: The border region around Chanthaburi and Pailin was for decades one of the great sources of ruby and sapphire.
Tone: Tone describes how light or dark a colour appears – from very light through medium to very dark.
Tourmaline: Tourmaline is a mineral group with an extraordinary range of colours – from red and pink through green to blue, often several colours in one crystal.
Transparency: Transparency describes how much light passes through a stone: transparent, semi-transparent, translucent or opaque.
Treatment: A treatment is any process other than cutting and polishing that alters a gemstone’s colour, clarity or durability – for example heating, filling fissures with oil, resin or glass, diffusion, or HPHT and irradiation in diamonds.
Window: A window is a pale, see-through area in the centre of a stone where you look through it instead of seeing colour.
Zambia: Zambia is today the world’s largest emerald producer.