The Gemstone Library
Gemstones, diamonds and jewelry, explained in plain English.
211 reference pages on how gems form, how they are graded and treated, where they are mined, and how people have worn them for 100,000 years.
Gem profiles
Start with the great gems
Properties, sources, treatments, value and care for each stone.
Gemstone profileRubyRuby is red corundum colored by chromium. Learn what makes a fine ruby, where rubies are mined, how they are treated and how to judge value.Gemstone profileSapphireSapphire is gem corundum in every color but red. Learn about blue and fancy sapphires, padparadscha, star stones, major sources, treatments and value.Gemstone profileEmeraldEmerald is green beryl colored by chromium and vanadium. Learn about jardin, Colombian and Zambian sources, oiling, trapiche stones and emerald care.Diamond guideThe Diamond 4CsHow the diamond 4Cs work, where GIA's grading system came from, and how color, clarity, cut and carat weight trade off against each other.October birthstoneOpalOpal is hydrated silica that can flash with play-of-color. Learn the types, Australian and Ethiopian sources, doublets and triplets, crazing and safe care.December birthstoneTanzaniteTanzanite is a blue-violet zoisite found only near Merelani, Tanzania. Learn about its 1967 discovery, heat treatment, trichroism, cleavage and care.June birthstoneAlexandriteAlexandrite is a chrysoberyl that changes from green in daylight to red in lamplight. Learn its history, sources, how to judge color change and spot synthetics.August birthstoneSpinelSpinel is a hard, bright gem that was long mistaken for ruby. Learn about its colors, famous historic stones, sources like Mogok and Mahenge, and care.Gemstone profileJade: Jadeite and NephriteJade is two minerals, jadeite and nephrite. Learn how they differ, how Burmese jadeite is graded, where nephrite comes from, and what A, B and C jade mean.
The library
Every section
Twelve sections, from mineralogy to metalsmithing.
Diamond Mines12 pages
- Diamond Mines of Angola
- Diamond Mines of Australia
- Diamond Mines of Botswana
- Diamond Mines of Brazil
- Diamond Mines of Canada
Gem Science27 pages
- The Mohs Hardness Scale
- Vickers Hardness Testing
- Refractive Index of Gemstones
- Specific Gravity of Gemstones
- Cleavage in Gemstones
Gem Cutting and Gem Regions13 pages
- Antwerp as a Gem Cutting Center
- Amsterdam Diamond Cutting
- Bruges and Early Diamond Cutting
- Idar-Oberstein Gem Cutting
- Gujarat and Surat Diamond Cutting
Before you buy
Guides people use most
Buying guideHow to Buy a GemstoneWhat to check before buying a colored gemstone: color, clarity norms by gem, cut, carat, treatments, synthetics, lab reports and return policies.Gem scienceGemstone Treatments ExplainedA plain guide to gem treatments such as heating, oiling, filling, dyeing, irradiation, diffusion and coating, with notes on stability and disclosure.Diamond guideHow to Tell if a Diamond Is RealWhich home diamond tests tell you something and which mislead, how thermal and electrical testers work, and why only a lab can spot lab-grown diamonds.Gem scienceThe Mohs Hardness ScaleHow the Mohs scale ranks scratch resistance from talc to diamond, why its steps are uneven, and what hardness means for gems worn every day.Diamond guideLab-Grown DiamondsHow lab-grown diamonds are made by HPHT and CVD, their history since the 1950s, how labs detect them, and what the 2018 FTC Guides say about disclosure.Jewelry careHow to Clean Jewelry SafelySafe ways to clean jewelry at home, which gems tolerate ultrasonic and steam cleaners, how to handle porous and treated stones, and when to see a jeweler.