Coloured gemstones and pearls
Where coloured stones come from, how they are treated, and what that means for disclosure, value and care.
Birthstones by Month: The Modern List, Alternatives and Care
The modern US birthstone for every month, with alternates, Mohs hardness and a care note for each stone, plus how the list began in 1912 and changed since.
Colombian Emeralds: Muzo, Chivor and the History of the Trade
Where Colombian emeralds are mined, the Green War and 1990 peace, Víctor Carranza's role, three-phase inclusions, oil and resin fillers, and origin reports.
Dyed and Irradiated Cultured Pearls: How to Identify Them
How dyed and irradiated cultured pearls are made, the signs at the counter, how labs separate them from natural-color black pearls, and what to disclose.
Gemstone Hardness: The Mohs Scale, Toughness and Stability
The Mohs hardness scale and its ten reference minerals, hardness of common gems, how toughness and stability differ, why dust scratches gems, and wear advice.
Tanzanite as a December Birthstone: How It Joined the List
Tanzanite became a December birthstone in October 2002, when AGTA added it alongside turquoise and zircon. The history, the other December stones and care.
Tanzanite: Where It Comes From and How to Buy It
Tanzanite is mined commercially only in Tanzania's Merelani Hills. How it is heated, graded and traded, and what the 2002 Tucson protocols changed.