Birthstones / December
December: Tanzanite, Turquoise, Zircon
Traditional: Turquoise, Lapis lazuli · Blue-violet (tanzanite); sky blue to green (turquoise); blue, colorless, golden (zircon) · Mohs 6 to 7 (tanzanite); 5 to 6 (turquoise); 6.5 to 7.5 (zircon)
What it is
Three blues. Tanzanite is zoisite from one area of Tanzania, heated from brown to blue, and cleaves, so a pendant stone more than a ring stone. Turquoise is a soft, porous copper mineral, usually stabilized with resin; much cheap 'turquoise' is dyed howlite or reconstituted powder. Zircon is a natural mineral (not cubic zirconia) with high brilliance; blue zircon is heated.
Care
Tanzanite: soap and water, no ultrasonic. Turquoise: dry cloth, no water or oils. Zircon: soap and water, avoid knocks.
Before you buy
Turquoise listings should say natural, stabilized or reconstituted; most are stabilized and that is fine. Tanzanite under a certain price is usually small or pale; lab-grown tanzanite does not exist commercially, but blue glass and synthetic forsterite are sold as look-alikes.
Sources: Jewelers of America modern birthstone list; GIA gem encyclopedia; FTC Jewelry Guides on treatment and lab-growth disclosure. Clasp & Lens does not appraise or grade stones; what a listing says is the supplier's statement.