The jewelry market grows ever more complex, which is why it’s important to be an informed customer—whether you’re shopping online or working directly with a jeweler. The following free online resources can improve your knowledge of gemstones, so you’re ready to make a smart investment when the time comes. Many of these may also be useful if you're a gem collector or professional appraiser.
Where to Go Online to Learn about Gems
This channel features tutorials on gemstone and precious metal testing and demonstrates the practical application of these methods.
Forgive the self-plug here, but we’ve got a wide variety of reader-friendly articles about gems and the jewelry industry with a focus on conflict-free stones and eco-friendly methods of production. Explore posts like Gem Hardness and Diamonds vs. White Sapphires to brush-up on some gemstone basics.
An Emeritus Professor at the College of Southern Nevada, Smigel has made her teaching materials on gemology available to the public.
A learning institute for professional gemologist training, the CIGEM is a fantastic resource for individuals interested in pursuing a career in gemology. You may be interested in subscribing to their quarterly newsletter.
Emporia State University offers 44 lectures and accompanying course notes on topics like gemstone identification and gemstone testing methods.
This database of public domain books on gems is an invaluable resource. The site even offers its own online reader.
Written by gemstone scholar Vincent Pardieu, this blog is for the reader interested in travel, local mining operations, and the origins of gemstones.
Looking for a spectroscopy resource? Check out John Harris’ lessons, reference charts, and illustrations on Gem Lab.
Created by FGAA Gemologist Edward Mendelson, this extensive channel features a compilation of gemology tutorials. Thoughtfully organized playlists make the browsing experience a breeze.
One of the world’s most trusted resources on gemstones, the GIA site features articles on the latest developments in the industry and a free gem encyclopedia.
This non-profit database for gem enthusiasts offers both basic and advanced tutorials on gemstones.
GemSelect.com – Gemstone Information Center
With hundreds of details articles, Gem Select is an expansive resource for information on gems.
For all things relating to gemstone magnetism, explore Kirk Feral’s research and reference charts on Gemstone Magnetism.
Gem Val helps users estimate the value of many kinds of gems using regularly updated pricing data. (Pricing data for certain gems requires a paid subscription, however.) The site also features information on historical prices.
With beautifully illustrated articles, Lotus Gemology provides detailed explanations of various principles in gemology.
This non-profit project features information on collector gemstones.
This branch of the Smithsonian Institution provides a stunning photo gallery of gemstones and minerals. Handy search filters allow you to view results by country origins and more.
Starla Turner is an experienced gemology instructor. Her engaging and informative videos may benefit the professional and hobbyist alike.
This site is especially suited for the professional gemologist or gem appraiser. Stone Group Labs offers advanced gemological testing services and global consulting. The site’s “Published Works” section features journal articles relevant to the trade.
Like the Farlang Education Center (see above), the Swedish Gem LAB is full of digitalized, non-copyrighted gemological books, a collection that offers both historical and scientific perspectives on gems.
Check out this site to access lecture notes and course materials from the department of Earth & Planetary Sciences of UC Berkeley.
This site offers gemology course notes on gemstone types, mining sources, and pricing and valuations—plus you can browse through over 6,000 photos of gemological specimens.
Courtesy of the University of Washington, full-length lecture notes and accompanying illustrations on minerals and gems are available to the public.
Visit the US Gemological Survey to learn more about the production of gemstones in the United States. You may also want to view their page on Minerals Information, which details the global supply and demand for minerals.
This free online gemology school and reference resource offers several engaging tutorials on gemology basics, including lessons on minerals, created and treated gemstones, and jewelry appraisals.
Have we missed anything? Let us know in the comments below if there's a resource that should be added to this list!
Photo: Alejandro Escamilla via Unsplash
Opals consist of hydrated silica and occur in rock fissures. Due to their structure, opals are considered mineraloids rather than minerals. Opals are the national gemstone of Australia but are also found in Ethiopia and Virgin Valley, Nevada.
Opals have been the subject of various lore. During the Middle Ages, opals were associated with great luck and believed to carry the properties of every gem whose color matched one of the many colors reflected in the opal. Opals were also believed to bestow the power of invisibility. By wrapping an opal in a bay leaf and holding it in your hand, you could avoid being seen—or so the story goes.
Love of opals and belief in their inherent goodness dramatically changed with the publication of Sir Walter Scott’s Anne of Geierstein in 1829. The book describes a character who dies shortly after her opal comes into contact with a drop of holy water and turns black. Shortly after the book's publication, opal sales dropped by 50% in Europe and remained low for the next 20 years.
The Different Types of Opals
Black/Dark Opals are the rarest and most valuable opals. Found in the Lighting Ridge in New South Wales, black or dark opals have a naturally dark background, which allows their colors and rainbow tones to appear more vibrant. This natural layer of potch (colorless opal) on the back of the stone varies in darkness; the darker the potch, the more vibrant the colors in the stone. The more vibrant the stone, the greater its value. Most black/dark opals are cut into ovals or teardrops.
White Opals or “milk opals” are light with a white body tone (as opposed to the black/dark body tone of the black/dark opals). Mined in southern Australia in the opal fields of Coober, Pedy, Mintabie, and Andamooka, white opals are the most common opals and therefore the least valuable--but they can still be quite pretty.
Crystal Opals can be light or dark and are partially transparent. Partial transparency may enhance the color (and value) of a stone. An opal with transparency may be referred to as a “white crystal opal” or “black crystal opal” depending on its body tone.
Boulder Opals form in ironstone cavities in Queensland. They’re typically cut with some solid brown ironstone remaining on the back; the ironstone backing functions like the dark potch on black/dark opals, allowing the colors in the opal to stand out vibrantly. Found in Quilpie and Winton, boulder opals vary greatly in size and may be found as small as a pea or as large as a car. These are the second most valuable opals and are distinct for their thin, colorful veins. Boulder opals tend to have a flat or undulating surface and are almost always cut in a freedom shape, which maximizes the size the of the stone.
Matrix Opals occur as a network of veins between crevices in the host rock (usually claystone or ironstone). An andamooka matrix opal is a kind of matrix opal that has been enhanced by soaking in a sugar solution and boiled in acid, a process that deposits carbon in the stone’s pores, creating a darker background. A natural oulder opal matrix is a matrix opal in its natural state; it consists of brown ironstone with small deposits of opal.
Polished Yowan Nut Opal
Yowan Nuts are found in Yowan in Queensland. These ironstone concretions resemble nuts, which can be cracked open to reveal a valuable opal in the center.
Synthetic Opals are made in a lab with opaline silica, whose structure is similar to that of natural opal. Gilson Opals are the most well-known lab-created opals. Synthetic opals generally show brighter colors, are larger, and have a more ordered array of colors. Numerous subgrains in synthetic opals produce a delicate snakeskin pattern.
Imitation Opals are made with colored tinsel set in clear plastic or epoxy. They’re generally not convincing to the untrained eye.
Doublets and Triplets are partially man-made stones that imitate black opals. Doublets and triplets consist of a slice of opal attached to a dark backing. In addition to being attached to a dark backing, triplets have a clear quartz or glass capping to magnify and protect the stone while giving it a rounded appearance.