September Birthstone
Sapphire — royal blue corundum; wisdom and nobility at the threshold of autumn.
September's birthstone is sapphire, the blue variety of corundum (Al₂O₃) coloured by iron (Fe²⁺/Fe³⁺) and titanium (Ti⁴⁺) charge transfer. While 'sapphire' most commonly refers to blue corundum, the term covers all non-red corundum — including yellow, pink, orange, green, and padparadscha (pink-orange). Blue sapphire is one of the most valuable coloured gemstones, with Kashmir sapphire (from the Zanskar range of India) commanding the highest premiums due to exceptional colour and historical rarity. Major modern sources are Sri Lanka (Ceylon sapphire), Madagascar, Kashmir, Myanmar, Australia, and Thailand. Sapphire rates 9 Mohs — the second hardest natural mineral — making it excellent for daily-wear jewellery.
Quick facts
- Item type
- Birthstone month
- Color range
- royal blue, cornflower blue, medium blue, dark blue, padparadscha (pink-orange), yellow, green
- Birthstone month
- September (traditional)
Blue Sapphire Colour and Chemistry
Blue sapphire's colour results from an intervalence charge transfer between adjacent Fe²⁺ and Ti⁴⁺ ions in the corundum structure — specifically between octahedral sites. This process absorbs yellow wavelengths (approximately 550–600 nm) and transmits blue. The intensity of blue depends on the Fe/Ti ratio and the distribution of these ions across specific lattice sites. The ideal blue sapphire colour is medium to medium-dark, vivid, pure blue — often described as 'cornflower blue' (Kashmir standard) or 'royal blue.' Kashmir sapphires from the Zanskar Range (discovered 1881, mined predominantly 1882–1887) show a distinctive silky, velvety blue caused by minute rutile inclusions that scatter light uniformly — producing a non-directional glow rather than a sharp point-source reflection. This 'sleepy' or velvety quality is the most coveted sapphire character and cannot be replicated by treatment.
Famous Sapphires and Sources
Kashmir sapphires from the Padder Valley mines (Zanskar, Ladakh region, India), mined for less than a decade in the 1880s, remain the world's most coveted sapphires by source premium: Kashmir sapphire with GIA origin report commands 3–10× the price of equivalent Ceylon sapphire. The mines produced for a short period before becoming economically exhausted; modern specimens on the market are antique or estate pieces re-entering circulation. Ceylon (Sri Lanka) sapphire is the most commercially significant source: Sri Lanka produces all colour varieties including the finest padparadscha, fine blue, and yellow sapphires. Madagascar (Ilakaka deposit, discovered 1998) became a major supplier of blue sapphire in the 2000s; Malagasy stones can be exceptional but lack the Kashmir/Ceylon premium. Australia (New South Wales) produces dark, inky blue sapphires used as commercial material. The Rockefeller Sapphire (62.02 ct, Ceylon) and Stuart Sapphire (104 ct, Sri Lanka) are historic examples.
Zodiac Connection: Virgo
September birthstones align with Virgo (the maiden), governing approximately August 23 to September 22. Virgo is an earth sign associated with precision, discernment, analytical thinking, and the harvest — the sign that presides over the transition from summer abundance to autumn organisation. Sapphire's traditional associations with wisdom, clear thinking, truth, and loyalty align with Virgo's qualities of precision and commitment to discernment. Medieval scholars and clergy favoured sapphire as the gem of truth and heavenly wisdom — associations that mirror Virgo's analytical, knowledge-seeking character. In Western gem astrology, sapphire was associated with Saturn — the planet of discipline, structure, and careful thought — values central to Virgo's archetype. The transition that September marks in the calendar (harvest, school returning, preparation) reflects sapphire's cool, measured clarity rather than summer's passionate heat.
Sources & further reading (2)
- gemological-institute — accessed 2026-05-08
- encyclopedia — accessed 2026-05-08
Frequently asked questions
Is the blue sapphire in Princess Diana's engagement ring a Kashmir sapphire?
No. The famous 18-carat oval blue sapphire in what was Princess Diana's and is now Princess Catherine's (Kate Middleton's) engagement ring is a Ceylon (Sri Lankan) sapphire. GIA examination has confirmed its Sri Lankan origin. It is set in 18-carat white gold with 14 round brilliant diamonds. Prince Charles (now King Charles III) selected it from a Garrard catalogue in 1981; at the time it was unusual for a royal engagement ring because it was a commercial catalogue item available to the public (this was noted in press at the time as unconventional). The ring became the world's most famous sapphire jewel when it passed to Catherine Middleton upon her engagement to Prince William in 2010. Fine Kashmir sapphires are significantly rarer than Ceylon sapphires and would not appear in a commercial catalogue.
What is the difference between blue sapphire and blue topaz?
Blue sapphire and blue topaz differ in mineral species, hardness, density, optical properties, and value. Sapphire is corundum (Al₂O₃, Mohs 9, SG 3.99–4.00, RI 1.762–1.770); topaz is Al₂SiO₄(F,OH)₂ (Mohs 8, SG 3.49–3.57, RI 1.619–1.627). Blue topaz is almost universally irradiated and heat-treated to produce its colours (Swiss Blue, Sky Blue, London Blue) and is far more common and affordable than fine sapphire. A fine 5-carat Kashmir or Ceylon sapphire can be worth $50,000–$500,000+; a 5-carat London Blue topaz retails for $100–$500. The colours overlap in the mid-blue range but sapphire's higher RI gives it more brilliance; topaz appears brighter and more glassy; sapphire's Kashmir variety has a distinctive velvety quality. Sapphire is significantly more durable and appropriate for high-wear jewellery.
Can sapphires be colours other than blue?
Yes. Sapphire refers to all gem corundum except red (ruby). The colour range includes: blue (most valued; iron-titanium charge transfer), yellow and orange (iron Fe³⁺), pink (chromium at low concentration), green (iron Fe²⁺ with Fe³⁺ combinations), purple/violet (combination of chromium and iron-titanium), colourless (no chromophores), and the unique padparadscha (a Sinhalese word meaning lotus flower, denoting a pink-orange blend of chromium and iron unique to Sri Lanka and a few other localities). Colour-change sapphires (typically blue in daylight, purple under incandescent) also exist. Padparadscha sapphire is prized as a distinct variety; genuine padparadscha — medium tone, pink-orange, neither dominantly pink nor orange — commands premiums of 3–10× equivalent blue sapphire. GIA and other labs issue origin reports for padparadscha.