Topaz is a hard, brilliant silicate that most people know as a blue stone, but its real story is more interesting: the blues on the market are overwhelmingly created in a lab from colorless topaz, while topaz's rarest and most valuable natural color is a warm pink-orange called imperial.
Hard, but mind the cleavage
At Mohs 8, topaz is the hardest common silicate and resists scratching very well. But hardness is not toughness: topaz has perfect basal cleavage, a single plane along which a sharp knock can split or chip it cleanly. It is durable in everyday jewelry with sensible care, but it is not indestructible, and cutters and setters must respect that cleavage direction.
The blue almost nobody digs up
Natural blue topaz exists but is pale and uncommon. The vivid sky, Swiss, and London blues you see everywhere start as colorless topaz that is irradiated and then heated to produce stable blue color. This treatment is routine, permanent, and accepted, and it is the reason blue topaz is so inexpensive for its size. Blue topaz is also a common December birthstone, while topaz overall shares November with citrine.
"Mystic" and coated topaz
Rainbow "mystic topaz" is colorless topaz with a thin metallic surface coating that produces an iridescent oil-slick effect. It is legitimate when disclosed, but the coating is only surface-deep and can scratch or wear over time, so it needs gentle care and should be priced as a coated novelty, not a natural color.
Imperial and precious topaz
The premium natural topaz is imperial (or precious) topaz: a warm orange to pink-orange to sherry color, historically from Ouro Preto in Brazil. Fine pink topaz, some of it produced by gently heating certain sherry-colored material, is also prized. These natural colors command far higher prices than treated blue.
Telling topaz from cheaper stones
Because "topaz" was long used loosely, beware old labels: "smoky topaz" is usually smoky quartz, and much yellow "topaz" in vintage jewelry is citrine. True topaz is denser and harder, with a higher refractive index, and a jeweler can separate them easily.
Caring for topaz
Clean topaz with warm soapy water and a soft brush. Avoid ultrasonic and steam cleaners, which can exploit the cleavage, and keep it away from sudden temperature changes and hard knocks. Some topaz colors can fade with prolonged strong sunlight, so do not store it in a sunny window. Coated "mystic" topaz needs especially gentle handling to protect its surface.
Topaz is a study in what "hard" really means. Enjoy inexpensive treated blue for its size and sparkle, seek natural imperial topaz if you want rarity, and in both cases respect the cleavage that its Mohs 8 hardness cannot protect against.
