Gemology Hub | Gemstone & Mineral Identification Guides

  Interested in gemstones and the science behind them? Gemology MCQs: Gemstones Study Guide offers a structured way to learn and review key gemology concepts through multiple-choice practice. The first edition includes 529 questions across 108 topics in a 177-page PDF , designed for beginner to intermediate learners. Questions cover gemstone formation, physical and optical properties, crystal shapes, inclusions, faceting, synthetic gems, imitations, enhancement, and identification. You’ll also find quizzes on many individual gemstones and varieties, including diamond, garnet, beryl, quartz, chalcedony, corundum, and tourmaline. A dedicated 50-question section on physical properties reviews topics such as hardness, cleavage, fracture, specific gravity, and carat weight. Answers and explanations support self-paced review. When a source question does not include a separate explanation, the guide identifies that clearly. Get the study guide The ebook is available as a digital PDF. V...

A gemstone can look different under two lamps without necessarily qualifying as alexandrite. Lighting changes the colours available to illuminate a stone. A narrow-spectrum lamp can therefore create a striking visual shift that needs careful interpretation. What makes alexandrite different? Alexandrite is a variety of chrysoberyl associated with a definite colour change caused by chromium. SSEF’s 2012 news slides compare this with a chrysoberyl that looked different under a particular LED but showed almost no main colour change between daylight and incandescent light. Why the comparison conditions matter A specialised lamp can emphasise only part of a gemstone’s response. The appearance under that lamp is interesting, but it should not replace a comparison under standard lighting conditions. The same caution applies to photographs whose lighting has not been explained. SSEF’s later public article reinforces the need to consider an appropriate colour change together with chromium-rela...

Radiocarbon research adds a time-related question to pearl testing: when did the sampled pearl material form? This can help investigate historical claims, but age and natural-versus-cultured formation are different questions. A recent pearl can be either natural or cultured. How the historical research worked SSEF’s 2013 article describes collaboration with ETH Zurich. A small amount of pearl material was removed and measured using accelerator mass spectrometry. The method used carbon-isotope information, including the increase linked to twentieth-century atmospheric nuclear testing. Unlike an X-ray image, this procedure consumes a sample. The article describes an early research project, so its sampling amount and service availability should not be assumed to apply to every current test. Why the environment matters Marine reservoir effects can influence the apparent age. Freshwater pearls may be especially difficult because older carbon from limestone can enter the growing pearl...

Some Kashmir sapphires are famous for a rich blue colour with a soft, velvety appearance. However, other deposits can produce sapphires that look similar. A beautiful visual effect is not enough to establish Kashmir origin. What the laboratory compares SSEF’s 2013 article discusses microscopic growth features, inclusions, chemistry and spectroscopy. Fine particles in some growth zones scatter light and contribute to the characteristic appearance. The shape and arrangement of internal features can provide useful evidence. The article specifically compares Kashmir and Madagascar material. It describes similarities as well as subtle differences and explains why the evidence must be considered together. A single inclusion or one chemical number should not be turned into a universal origin rule. Origin does not guarantee quality Every deposit produces a range of material. SSEF stresses that a Kashmir label does not automatically mean an exceptional stone. Colour, transparency, cut an...

Some blue cabochons in antique jewellery may look like turquoise but consist of a different material. Odontolite is one historical example. It is associated with fossil dentine and was also marketed under names such as bone turquoise, which can easily cause confusion. The historic brooch investigation SSEF’s 2012 article describes six brooches containing mostly odontolite, along with some actual turquoise and glass. Microscopic examination and Raman analysis helped separate the materials. The finding shows why matching colour across a jewel does not prove matching identity. How odontolite becomes blue Odontolite contains mainly fluorapatite. The article explains that heating can change the state of manganese traces and create a blue appearance. This is different from simply assuming that every turquoise-coloured material is the mineral turquoise. Surface pores, banding and, in some specimens, features associated with ivory structure contributed to the investigation. Such observa...

Sapphire is often associated with blue, but the corundum family offers a much broader colour range. Yellow, pink, violet and green sapphires are examples of the fancy colours discussed in SSEF’s 2012 Facette. A colourless ideal composition can become colourful through very small changes. What produces the colours? Pure corundum is aluminium oxide. Small amounts of other elements can enter its crystal structure and change which wavelengths it absorbs. Chromium contributes to red ruby colour, while iron and titanium are important in many blue sapphires. The colour depends on more than the total amount of one element. Its chemical state, combinations with other elements and colour centres in the crystal can all matter. Some corundum also shows different colours or shades in different viewing directions, a property called pleochroism. Why colour names have boundaries SSEF discusses the difficulty of separating nearby colour categories, such as pink sapphire and ruby. Variety names i...

EDXRF stands for energy-dispersive X-ray fluorescence. It is a laboratory method for examining chemical elements in a gem without drilling a sampling hole. The long name describes a useful principle: elements emit characteristic X-rays when excited. How the measurement works An instrument exposes the sample to X-rays and measures the energies of the X-rays emitted in response. Peaks in the resulting spectrum help identify elements. With suitable calibration, the measurements can also provide information about their amounts. SSEF’s 2011 article explains why this approach is useful for both loose and mounted gems. The article describes the introduction of a particular instrument at that time; it is not a statement about the laboratory’s entire current equipment. What chemistry can help explain Chemical data can support gem identification, colour research and some geographic-origin investigations. It becomes more informative when combined with knowledge of the material and reliable...

Spinel is more than a red gemstone. Natural examples can be pink, violet, blue and many other shades. Its colour range reflects small differences in chemistry, while its crystal shape and geological setting add further interest for collectors. The role of colour-producing elements SSEF’s 2011 overview describes chemically pure spinel as colourless. Chromium can contribute pink and red, while iron, vanadium and occasionally cobalt influence other colours. The mix and amounts matter, so there is no single colour for all spinel. The article discusses classic and newer sources, including Myanmar, Sri Lanka, Tajikistan, Vietnam, Madagascar and Tanzania. These are historical source examples, not a complete list of every occurrence. Crystal shape is another clue Spinel has a cubic crystal structure and commonly forms octahedra, which resemble two pyramids joined at their bases. Twinning can create interesting shapes. A rough crystal can therefore be attractive even before it is faceted...

A pink sapphire with a violet component may become a cleaner pink after heating. Detecting this change can be difficult when the heating leaves little obvious damage inside the stone. The word low-temperature is relative: the temperatures involved are still extremely high. What the experiments showed SSEF’s 2010 article describes research on pink sapphires from Madagascar and East Africa. Heating around 800–1000°C could reduce the blue component. The researchers also studied samples at several lower and higher experimental temperatures. The important lesson is that familiar microscopic signs of intense heating can be scarce after lower-temperature treatment. A stone that lacks melted-looking inclusions is not automatically proven unheated. Zircon inclusions as evidence The study investigated zircon inclusions with Raman spectroscopy. Heating could alter their crystal condition and the shape of their spectral peaks. Measuring these changes provided evidence that was less obvious ...

A ruby’s inclusions can offer clues about its geological history. However, similar-looking inclusions can occur in stones from different places. Early research on rubies from Montepuez, Mozambique, makes this limitation especially easy to understand. What SSEF observed In its 2010 Facette, SSEF described a preliminary investigation of six small samples. Observations included twinning, fissures, crystal inclusions and fine rutile features. The article noted that the internal appearance could resemble Mogok-type rubies from Myanmar. This similarity is valuable for learning, but it does not make the two origins interchangeable. An inclusion pattern associated with a famous deposit may also occur elsewhere. The 2012 SSEF news slides reinforce this point with further Mozambique ruby examples. Why one inclusion cannot locate a mine A laboratory compares multiple microscopic features with chemical and spectroscopic evidence and documented reference samples. The strength of an origin op...

A synthetic spinel is grown by people but has the identity of spinel. It is different from a material that only imitates spinel’s appearance. Flux-grown red spinel is a useful example of why a correct mineral identification does not always establish natural origin. Why routine measurements may overlap SSEF’s 2009 study reported flux-grown red spinels with refractive index and density similar to natural spinel. Their attractive appearance and fluorescence were also insufficient for reliable separation. A familiar result on a basic gem test therefore did not settle the formation question. What the researchers examined Microscopy revealed cavities containing flux residues, sometimes with gas bubbles, and a metallic flake in one specimen. Chemical and spectroscopic observations helped support the interpretation. Brown material inside a fissure must not automatically be labelled flux. Natural spinel can contain other brownish substances, and a similar-looking feature may have a diffe...

The outside of a pearl can look convincing while its centre holds the most useful identification clues. X-ray microtomography, often called micro-CT, helps laboratories examine these hidden structures in three dimensions without cutting the pearl open. From a flat image to virtual slices A conventional radiograph projects internal features onto a flat image. Structures can overlap in that view. Micro-CT uses multiple X-ray views to reconstruct the interior, allowing the analyst to inspect virtual sections in different directions. SSEF’s 2009 article describes how this approach helped investigate pearl growth features. It highlights difficult beadless cultured pearls, for which a clearer view of the central region can be particularly useful. What can the images show? Cavities, fissures and growth structures can become easier to understand when viewed from several angles. The analyst can ask whether a line belongs to one cavity or whether several different features overlap. This p...

Beryllium diffusion is a sapphire treatment, but detecting a trace of beryllium is not automatically the same as proving that treatment. The context of the result matters. This distinction is especially useful when reading claims about highly sensitive chemical tests. A natural example in SSEF research In its 2008 Facette, SSEF described a sapphire–chrysoberyl intergrowth from Madagascar. The study confirmed that low trace amounts of beryllium can occur in natural untreated sapphire. The researchers discussed its relationship with other elements and possible tiny inclusions. That finding does not mean beryllium diffusion is undetectable. It means a laboratory must distinguish natural occurrences from evidence consistent with artificial introduction. A simple present-or-absent rule loses that important detail. What a laboratory considers Sensitive chemical methods can examine very small concentrations and differences within a stone. Microscopic features and the distribution of ch...

A gemstone’s colour depends partly on which wavelengths of light it absorbs and which remain available to reach our eyes. UV-Vis spectroscopy measures this interaction. It turns a colour observation into a pattern that a gemologist can study and compare. What is an absorption spectrum? An absorption spectrum shows how strongly a material absorbs light at different wavelengths. Peaks and bands can provide information about colour-producing elements or other features inside a crystal. Some useful information lies outside the light we can see. SSEF’s 2008 article explains a portable instrument developed for testing away from the main laboratory. It discusses applications to colour research and supporting evidence for sapphire origin analysis. The historical equipment specifications should not be assumed to describe all instruments used today. Why orientation can matter The spectrum must be measured and interpreted under suitable conditions. The observed colour and absorption behavi...

An intense blue or green-blue tourmaline can be beautiful without revealing the country where it formed. Copper-bearing tourmalines from Brazil and parts of Africa can have similar appearances. Colour is therefore an unreliable shortcut for geographic origin. What trace elements can reveal SSEF’s 2007 article compares material from Brazil, Nigeria and Mozambique. It discusses trace-element patterns, including lead, gallium and bismuth, studied with methods such as LA-ICP-MS. These are small chemical clues rather than features visible to the naked eye. The article notes substantial overlap in chemical composition. Useful distinctions emerge from careful comparisons and data interpretation, rather than a rule that one element always identifies one country. Why reference samples matter A laboratory needs reliable samples from known sources to interpret the chemistry of an unknown stone. A measurement becomes much more useful when it can be compared with a documented reference colle...

Melee diamonds are small diamonds used in groups, often in watches and jewellery. Checking thousands of tiny stones creates a different practical problem from grading one large diamond. A laboratory needs a clear plan for what to inspect and how to report the result. Why use a representative sample? SSEF’s 2007 article explains quality control using a representative sample from a lot. This approach depends on a suitably defined, reasonably homogeneous batch and clear quality criteria. It does not mean that every stone has received an individual grade. Colour, clarity and cut still matter. Tiny size makes some observations harder, so the way results and uncertainty are communicated is important. A sample report should be read in the context of the sampling plan. What does AQL mean? An acceptable quality level, or AQL, is used with a sampling plan to decide whether a lot meets an agreed acceptance rule. The buyer’s chosen rule affects the outcome. It should not be read as a guaran...

Dye can change a gemstone’s appearance while leaving its underlying mineral identity the same. A blue quartz specimen is still quartz, but its colour may need a treatment description. Mineral identification and colour authenticity therefore answer different questions. What the historical study examined SSEF’s 2006 article summarised Pierre Lefèvre’s work on colouring substances and methods for recognising them in gems. The study compared different observations and analytical methods. Its main educational message is that reliable identification requires evidence from more than one approach. What each method contributes Magnification can help examine where colour appears in a stone. Spectroscopy studies how the material interacts with light. Chemical analysis may provide additional information in some cases. A useful conclusion comes from bringing the relevant results together. A negative result in one test is not the same as proof of untreated colour. The dye might be difficult t...

An eye-catching inclusion can make a resin specimen seem like an extraordinary fossil. However, two questions must be answered: what is the surrounding material, and how did the inclusion get inside it? A natural resin can contain an object added by people. The SSEF investigation In a case reported in 2006, a collector submitted a resin piece containing a well-preserved lizard. Spectroscopy, microscopic observations, X-ray imaging and specialist advice were considered together. SSEF concluded that a modern lizard had been artificially embedded in recent natural resin. Why one result was not enough The initial infrared result supported natural resin but did not settle every possible resin identity. The investigation illustrates a general lesson: a test can answer one part of a question while leaving another part open. For example, confirming that a mineral is natural would not prove that two pieces were never glued together. In the same way, confirming resin chemistry does not in...

A red bead is not automatically natural-colour precious coral. Gem coral includes different animal skeleton materials, and the market also contains dyed products and imitations. Understanding the material and understanding its colour are two separate parts of identification. Different corals have different structures SSEF’s 2005 overview distinguishes calcitic precious coral, aragonitic blue coral and corals with horn-like organic skeletons. Their structures and physical properties differ. Fossilised coral may also have undergone mineral replacement, so it should not be treated as identical to recent coral. Clues to dye and resin Dye may collect in pores, fissures or other open spaces. Resin may appear as a different substance within these areas. Drill holes can sometimes expose useful clues that are hidden on a polished outer surface. These observations are clues, not a complete home test. A clean-looking surface does not prove natural colour. SSEF describes combining microscop...

Pezzottaite is a pink gem mineral connected to the beryl group. Early material was sold under names such as raspberry beryl, but testing showed that the name did not fully describe the mineral. Its story is a good example of why a new colour does not automatically mean a new gem variety. What made the material unusual? SSEF’s 2004 report discusses samples from Madagascar and material reportedly from Afghanistan. The researchers noticed optical and density values that differed from ordinary beryl. Chemical and crystal-structure studies then showed the importance of caesium and lithium. The mineral was approved as pezzottaite in 2003 and named for mineralogist Federico Pezzotta. Although related to beryl, it is a distinct mineral species. The crystal structure matters just as much as the attractive pink colour. Why identification needs several tests A pink stone could belong to several mineral families. Colour alone cannot separate pezzottaite from every pink tourmaline or pink be...

Natural and cultured pearls both form inside molluscs. The key difference is whether people started the process. An imitation pearl is a manufactured lookalike. These three names describe different things, even when the beads look similar in a necklace. How a pearl begins A natural pearl forms without human intervention. A cultured pearl develops after a farming procedure, often involving a small piece of mantle tissue. That tissue can form a pearl sac, which deposits pearl material. Some cultured pearls grow around an inserted bead; others grow without one. Nacre, also called mother-of-pearl, contains very thin mineral layers. Their interaction with light helps create a pearl’s attractive sheen. A beadless cultured pearl is still cultured: the absence of a bead does not remove the human role in its formation. Why appearance is not enough Roundness, colour and lustre do not reliably tell you whether a pearl is natural or cultured. SSEF’s 2004 article explains the importance of e...

A mineral collection is more useful when each specimen has a clear record. A small label can keep the name, source and collecting history together. Albite (pericline), Ziller valley, Austria; specimen about 10 × 5 cm. Photo: Didier Descouens, CC BY-SA 4.0 , via Wikimedia Commons . Image unchanged. Why locality matters The Smithsonian mineral sciences collections organize specimens using details such as locality and catalog number. A home collector can use a simpler version of this idea. The place a specimen came from is part of its story. A practical label template Collection number: use your own unique code, such as M-001. Mineral name: write the best supported identification. Add “possible” or “unconfirmed” when needed. Locality: copy the place exactly as supplied. Keep mine, district, region and country details if known. Source and date: record who supplied it and when you acquired it. Size and photo: measure it without forcing fragile crystals. Photograph it beside a ruler. No...

The rock cycle explains how rocks change over time. There are three main rock groups: igneous, sedimentary and metamorphic. An andalusite specimen. Photo: Moha112100, CC BY-SA 3.0 , via Wikimedia Commons . Image unchanged. Igneous rocks: cooling from melted rock Magma is melted rock below the surface. When melted rock cools and becomes solid, it forms igneous rock. Sedimentary rocks: pieces become rock Weathering breaks rocks into smaller pieces. Water, wind or ice can move these pieces. Sediment builds up in layers. Compaction and cementation can turn it into sedimentary rock. Metamorphic rocks: change without melting Heat and pressure can change a solid rock into metamorphic rock. Melting is a different process. If rock melts, it becomes magma and may later form igneous rock. Does every rock follow the same path? No. The rock cycle is a model with many possible paths. A rock can be weathered, buried, changed or melted. It does not have to pass through all three groups in a fixed orde...

A pallasite meteorite brings two very different materials together: silicate minerals and metal. It is a striking reminder that minerals are found beyond Earth. A pallasite meteorite displayed in Greensburg, Kansas; this is not the Imilac specimen discussed below. Photo: Michael Adams, CC BY-SA 4.0 , via Wikimedia Commons . Image unchanged. What is inside a pallasite? Pallasites contain iron-nickel metal and the mineral olivine. Some olivine crystals look yellow-green. In a thin cut slice, light can pass through suitable crystals while the surrounding metal stays opaque. Where did they come from? These meteorites formed inside early asteroid bodies. As some bodies heated and melted, heavier metal moved toward the center while rocky material formed outer layers. Pallasites help scientists study the mixing of these materials. Is the story only about a core boundary? No. An older explanation placed their formation near the boundary between an asteroid's metal core and rocky mantle. Re...

A high Mohs number does not answer every question about a gemstone. For everyday jewelry, you also need to think about breakage and the stone's response to heat and chemicals. Moonstone is a feldspar gem that needs gentle care. Photo: Simon Eugster, CC BY-SA 3.0 , via Wikimedia Commons . Image unchanged. Three different questions Property Simple meaning Hardness How well does the surface resist scratches? Toughness How well does the material resist chips and breaks? Stability How does it respond to heat, light, moisture and chemicals? GIA explains these three parts of gem durability in More than the Mohs Scale . Why the Mohs scale is only one clue The scale compares scratch resistance. Its numbers are not evenly spaced. A stone at 10 is not simply twice as hard as one at 5. The number also does not measure resistance to a sudden impact. Can diamond break? Yes. Diamond resists scratching extremely well, but a hard blow can chip or split it. Cleavage describes directions in a crystal...

Moonstone looks beautiful, but cleaning it roughly can cause damage. This simple guide explains how to care for a known moonstone gem in jewelry. Moonstone is a feldspar gem that needs gentle care. Photo: Simon Eugster, CC BY-SA 3.0 , via Wikimedia Commons . Image unchanged. The gentle cleaning method Check the setting first. If the gem is loose or cracked, let a jeweler inspect it before cleaning. Use warm water with a small amount of mild soap. Gently clean with a soft brush. Avoid pressing hard around the stone. Remove the soap gently and dry with a soft cloth. GIA recommends warm soapy water for moonstone. It advises against both ultrasonic and steam cleaners. See the GIA moonstone care and cleaning guide . Why moonstone needs care Moonstone has a Mohs hardness of 6–6.5, but its toughness is poor. Two cleavage directions make it vulnerable to breaking from a hard blow. High heat and sudden temperature changes can also cause breaks. Before wearing a moonstone ring A ring is more exp...

A–Z Minerals: A — Andalusite. Andalusite is an interesting mineral for both geology students and crystal collectors. Its shape and the rocks around it can tell a useful story. An andalusite specimen. Photo: Moha112100, CC BY-SA 3.0 , via Wikimedia Commons . Image unchanged. What is andalusite? Its formula is Al 2 SiO 5 . Kyanite and sillimanite have the same chemical formula, but their atoms are arranged differently. Minerals like these are called polymorphs. Simple andalusite properties Crystal system: orthorhombic. Hardness: about 6.5–7.5 on the Mohs scale. Specific gravity: about 3.13–3.16. Streak: white. Shine: glassy. Shape: crystals may be long, with a nearly square cross section. Pink, green, gray and other colors occur. A crystal may also contain many inclusions, so transparency varies. The Handbook of Mineralogy gives the mineral data and occurrence details. How does andalusite form? It commonly forms when clay-rich rocks are changed by heat near an intrusion of molten...

A–Z Minerals: A — Albite. A pale crystal beside another mineral may look unimportant. Albite is worth a closer look. It is a common feldspar that helps us understand many rocks. Albite (pericline), Ziller valley, Austria; specimen about 10 × 5 cm. Photo: Didier Descouens, CC BY-SA 4.0 , via Wikimedia Commons . Image unchanged. What is albite? Albite is the sodium-rich end member of the plagioclase feldspar series. Its ideal formula is NaAlSi 3 O 8 . It has a triclinic crystal structure. In simple terms, this describes how its atoms are arranged. Albite properties at a glance Hardness: 6–6.5 on the Mohs scale. Color: commonly white or gray; other pale colors occur. Streak: white. Luster: glassy, sometimes pearly on cleavage surfaces. Specific gravity: about 2.60–2.65. Breakage: brittle, with strong cleavage directions. Where does it form? Albite occurs in granite, pegmatites and several other rocks. It also grows in some mineral veins. Quartz and mica may occur with it. Its name ...

  G7 Ban on Russian Diamonds: How Sanctions Are Reshaping the Global Rough Diamond Supply Chain in 2026 Updated: September 2026 The global diamond industry has changed considerably since the G7 countries began restricting Russian-origin diamonds. When I first wrote about this subject a few years ago, one of the main concerns was whether removing Russian rough diamonds from major Western markets would create shortages and increase diamond prices. The situation today is more complicated. Russian diamonds remain an important part of world production, but the G7 and European Union restrictions have changed how diamonds are imported, documented, traced and traded. At the same time, the natural diamond industry is facing other pressures, including weaker demand in some major markets, high inventories, competition from laboratory-grown diamonds and changing international trade conditions. Therefore, the impact of the Russian diamond ban should no longer be viewed simply as a question of d...

Comparison of Emeralds from the Chitral District, Pakistan, with other Pakistani and Afghan Emeralds" by Hanser et al. (2023), suitable for gemology students: 🔷 Origin and Location Emerald Deposit : Chitral District, north-western Pakistan (discovered in 2021) Geological Zone : Outside the traditional “ Emerald Belt ” ( Indus Suture Zone ) Host Rocks : Quartz- and mica-rich metapelites of the Arkari Formation , intruded by pegmatitic leucogranite 🪨 Rock Types and Formation Chitral emeralds form in schist-hosted environments Hosted in quartz- and mica-rich metamorphic rocks Similar to emeralds in Afghanistan's Panjshir and Swat (Pakistan) , but geochemically distinct 🎨 Color and Diaphaneity Colors : Light green to dark green Transparency : Mostly transparent; higher-quality than earlier samples Notable : Deeper-colored samples show potential for gem trade 🔍 Inclusions Chitral Inclusions : Two-phase inclusions (gas + liquid...