Blue Gemstones Guide: Sapphire, Tanzanite, Aquamarine & Topaz

Blue is one of the most requested gemstone colours, and buyers searching for "a blue stone" without a species in mind are usually choosing between these four — each occupying a genuinely different price tier and durability profile.

Sapphire — the hardest and most valuable

At 9 on the Mohs scale, sapphire is by far the most durable of the four and, in fine unheated quality, the most expensive per carat. See our full sapphire guide — colour ranges from pale to deeply saturated royal blue, with origin (Kashmir, Burma, Sri Lanka) a major price driver at the top end.

Tanzanite — rarer, softer, single-source

Tanzanite shows a striking violet-blue that shifts with the angle of view (pleochroism), but at 6-7 Mohs it's noticeably softer and more brittle than sapphire — better suited to occasional wear or a protective setting than an everyday ring, see our Mohs hardness guide. It's also geologically rare in a way sapphire isn't: essentially all tanzanite comes from a single mining area near Mount Kilimanjaro, Tanzania, which supports genuine scarcity claims that most gemstones can't make.

Aquamarine — accessible, clean, forgiving

A paler, cooler blue than sapphire or tanzanite, aquamarine (beryl, the same species as emerald) is comparatively affordable, typically very clean (eye visible inclusions meaningfully hurt value more than in most coloured stones), and at 7.5-8 Mohs durable enough for regular wear. It's the practical, budget-conscious choice among the four.

Blue topaz — abundant, inexpensive, always treated

Natural blue topaz is genuinely rare; nearly all blue topaz on the market today is colourless topaz that has been irradiated and heat-treated to produce blue — a standard, stable, disclosed treatment (see our treatments guide), not a red flag. At 8 Mohs it wears well daily and is by far the least expensive of the four, making it a popular choice for large statement pieces where sapphire or tanzanite at the same size would be prohibitively costly.

Choosing between them

For maximum durability and investment-grade rarity: sapphire. For a genuinely rare, single-source stone with a distinctive violet-blue, worn with some care: tanzanite. For a clean, affordable, durable everyday blue: aquamarine. For the biggest visual impact per pound spent: blue topaz.

Related reading

• Sapphire buying guide
• Mohs hardness scale: which gemstones are safe for everyday wear
• How gemstones are priced