September Birthstone: Sapphire, Beyond Blue

By Lisa Chen, Founder · July 16, 2026

Short answer: September's birthstone is sapphire — and sapphire is not a blue stone. It is the mineral corundum, and it comes in every color except red, because red corundum gets its own name: ruby. Once sapphire is a species rather than a color, a yellow sapphire stops sounding like a contradiction, and the two questions that matter — how was it treated, and did it come from the ground or a lab — move to the front.

What a sapphire actually is

Corundum is composed only of aluminum and oxygen, and in its purest state, the GIA notes, it is actually colorless. Everything you find beautiful about a sapphire is a rounding error in the chemistry — a few hundredths of a percent of iron and titanium turns corundum blue.

Corundum is the species, with two named varieties. Red corundum is ruby; everything else — including colorless — is sapphire. The GIA states it plainly: "Red corundum is known as ruby and all other colored corundum (including colorless, or white sapphire as it is known in the trade) is sapphire." There is no third category.

The color range, honestly laid out

Sapphires that are not blue have a trade name: fancy sapphires. The range, as the GIA describes it:

What you see	What it is called	Worth knowing
Blue, greenish to violetish	Blue sapphire	Color drives most of a sapphire's value.
Pink, orange, yellow, green, purple, violet	Fancy sapphire	Same mineral, different trace elements — the GIA lists these exact colors.
Colorless	White sapphire	Pure corundum. Once popular as diamond imitations, per the GIA.
A mix of pink and orange	Padparadscha	Named after the lotus flower. The GIA calls it "extremely rare and collectible," typically far higher in value.
Red	Ruby — not sapphire	The one color that leaves the category.

Two caveats the table cannot carry. "Fancy" is not a quality grade — it only means "not blue." And padparadscha is contested: the GIA notes its definition "has always been debated," so treat that label as something to see documented.

Why sapphire survives a life you actually live

The USGS defines hardness as a gemstone's resistance to scratching, measured against a standard scale of ten minerals — the Mohs scale, developed by the Austrian mineralogist F. Mohs in 1822. The USGS lists sapphire at 9 and diamond at 10. Quartz is 7.

That last number matters. Ordinary dust contains quartz, so anything below 7 is slowly sanded by the world it lives in. At 9, corundum outranks nearly everything it meets.

But hardness is only half of durability, and the half people over-quote. Hardness resists scratching; toughness resists breaking. Sapphire is good at both: the GIA states the September birthstone "has excellent toughness and no cleavage, which is a tendency to break when struck," making it "a great choice for rings and other mountings subject to daily wear." That is why sapphire ends up in rings worn for decades. Not romance. Crystallography.

That everyday-wear logic is what our everyday pieces are built around — and the same scrutiny applies to us: our gold is 18k plating over a stainless steel base, not solid gold.

The treatment picture, stated plainly

Sapphires are usually treated. The GIA is direct: "A large amount of the sapphire on the market, both blue and fancy colors, has been treated to alter its color by heat or by lattice diffusion," and "heat treatment is common — and the results permanent — so it is well accepted in the trade."

That is not a warning. A heated sapphire is not a fake sapphire — Sri Lanka's milky white "geuda" sapphires have been heat treated to a rich blue for centuries, above-board. Heating affects rarity, not authenticity: the GIA notes that for fine-quality sapphire, lab confirmation of no heat adds to value.

The less common ones change how you live with the stone:

• Lattice diffusion. Per the GIA, heat and chemicals diffuse an element into the stone to artificially change its color. It often looks vivid but is worth less than heated sapphire, and the color is sometimes so shallow it could be removed if the stone were chipped or recut.
• Fracture filling and dyeing. These "may require special care," per the GIA — such stones can be damaged by even mild acids like lemon juice.

None of this is a reason to avoid sapphire — it is a reason to ask, and you are not being difficult by asking. Under the FTC's Jewelry Guides, failing to disclose a treatment is unfair or deceptive when it is not permanent, creates special care requirements, or significantly affects value. The disclosure is owed to you.

Lab-grown sapphire is real sapphire. A simulant is not.

Lab-grown sapphire is corundum — aluminum oxide grown under controlled conditions instead of geological ones, with the same hardness, chemistry, and optical behavior. That is not marketing, it is the legal standard. The FTC's Jewelry Guides state it is unfair or deceptive to use "laboratory-grown" or "synthetic" with a natural stone's name "unless such product has essentially the same optical, physical, and chemical properties as the stone named." A seller may call it lab-grown sapphire because it genuinely is sapphire.

A simulant is a lookalike. Cubic zirconia and moissanite are different materials standing in for another stone's look. A blue cubic zirconia is not a blue sapphire in any sense except appearance. CZ and moissanite are simulants, not diamonds.

The FTC requires the distinction be visible rather than mumbled: "laboratory-grown," "imitation," or "simulated" must immediately precede the stone's name with equal conspicuousness, so the product is not passed off as a mined gem. "Faux," the Guides note, is not adequate disclosure. So lab-grown sapphire being cheaper is not suspicious — what should make you pause is a listing that says "sapphire" and then goes vague.

How to buy and care for it without guessing

• Ask what the stone is, and how it was treated. Mined, lab-grown, or simulant — three different answers. The GIA's advice: "Before you buy a sapphire, always ask if it is treated and by what method." For a significant stone, it suggests a lab report when in doubt.
• Clean it simply. Warm, soapy water is always a safe choice, per the GIA. Ultrasonic and steam cleaners are usually safe for untreated, heat-treated, and lattice diffusion–treated stones — but fracture-filled or dyed material should only get a damp cloth. Which is why the treatment question is not academic.

Where September's claim to sapphire comes from

The modern US birthstone list is a trade convention, not an ancient inheritance. Jewelers of America — which calls itself the originator of the US birthstone jewelry list — dates the official list to 1912, when the trade association that became today's JA established it. Stones have been added since. September's entry stayed simple: sapphire, alone, no alternate.

Sapphire also carries a long train of symbolism — sincerity, truth, faithfulness, nobility, and in medieval Europe an association with heaven. Stated the way it deserves: that is cultural tradition and history, the meaning people assigned to a blue stone over centuries. It is not a claim that a sapphire will do anything for your health, luck, relationships, or character.

Frequently asked questions

Is sapphire always blue?

No. Sapphire is the mineral corundum, and per the GIA, sapphires come in every color except red — red corundum is called ruby. Sapphires that are not blue are fancy sapphires, and the GIA lists their colors as pink, orange, yellow, green, purple, and violet. Colorless corundum is white sapphire.

How hard is sapphire, and can I wear it every day?

The USGS places sapphire at 9 on the Mohs scale of scratch resistance, with diamond at 10 and quartz at 7. Hardness is only part of durability: the GIA states the September birthstone also has excellent toughness and no cleavage, making it a great choice for rings and other mountings subject to daily wear.

Are most sapphires treated?

Treatment is common. The GIA states that a large amount of the sapphire on the market, both blue and fancy colors, has been treated to alter its color by heat or by lattice diffusion, and that heat treatment is permanent and well accepted in the trade. A heated sapphire is still a sapphire. Less common treatments such as fracture filling and dyeing may require special care, so always ask.

Is lab-grown sapphire real sapphire?

Yes. Lab-grown sapphire is corundum with the same chemical, physical, and optical properties as mined sapphire — a legal requirement, not a marketing line. The FTC's Jewelry Guides state it is unfair or deceptive to use terms like "laboratory-grown" or "synthetic" with a natural stone's name unless the product has essentially the same optical, physical, and chemical properties as the stone named.

What is the difference between a lab-grown sapphire and a simulant?

A lab-grown sapphire is sapphire. A simulant only looks like one. Cubic zirconia and moissanite are different materials that imitate another stone's appearance — they are simulants, and they are not diamonds either. The FTC's Jewelry Guides require words like "laboratory-grown," "imitation," or "simulated" to immediately precede the stone's name with equal conspicuousness.

Sapphire is a mineral, not a color, and the questions worth asking are what the stone is and how it was treated. For more, see our guides on October's birthstone, opal and tourmaline and August's birthstone lineup, or browse our rings collection.

If you want to wear September’s stone rather than read about it, our Personalized Cross & Birthstone Necklace is made in a September version — 18k gold plating over a 316L stainless steel base, built for daily wear. The stones are cubic zirconia, not mined gems, and the product page says so.