October Birthstone
Opal and tourmaline — October's two birthstones span fire-play and the full colour spectrum.
October has two modern birthstones: opal and tourmaline. Opal (SiO₂·nH₂O) is a hydrated silica mineraloid that displays play-of-colour — spectral flashes produced by diffraction of light from a regular array of silica spheres. Tourmaline is a boron silicate mineral group covering the widest colour range of any gem: red (rubellite), blue (indicolite), green, watermelon (pink-and-green in the same crystal), Paraíba (neon blue-green), and more. Both stones celebrate October's transitional quality: opal's fire and spectral play evoke the autumn leaf colours; tourmaline's multi-colour range represents the full palette of the season. Opal has been the traditional October stone since at least the 1912 ANJA list; tourmaline was added by AGTA in 1952 as an alternative.
Quick facts
- Item type
- Birthstone month
- Color range
- white/black with spectral play (opal), red (rubellite tourmaline), blue (indicolite), green, pink, watermelon, Paraíba neon blue-green
- Birthstone month
- October (traditional)
Opal's Play-of-Colour
Precious opal displays 'play-of-colour' — flashing spectral colours that change as the stone is moved. This phenomenon is produced by diffraction of light from a regular three-dimensional lattice of submicroscopic amorphous silica spheres (diameter approximately 150–400 nm) stacked in ordered layers within the opal structure. When sphere size and regular spacing match visible light wavelengths (400–700 nm), they diffract light into spectral colours. Larger spheres produce red and orange flashes; smaller spheres produce blue and violet. The arrangement of sphere domains within the stone determines the pattern of play-of-colour (pinfire, broad flash, harlequin — the rarest and most valued pattern). Black opal from Lightning Ridge, New South Wales, Australia, is considered the finest: the dark body colour (from carbon or iron oxide trace elements) increases the contrast of the spectral colours, making them appear more vivid against the dark background. Ethiopian opal from the Wollo Province has been commercially significant since the 2000s.
Tourmaline's Colour Range
Tourmaline is not a single mineral species but a group of boron silicates with the general formula (Na,Ca)(Li,Mg,Fe²⁺,Fe³⁺,Mn,Al,Cr)₃Al₆(BO₃)₃Si₆O₁₈(OH,F)₄ — the complex formula explains its extraordinary colour range. Elbaite is the primary gem species (Li,Na,Al); rubellite (red to pink elbaite), indicolite (blue to blue-green), verdelite (green), and Paraíba tourmaline (copper-bearing, neon blue-green) are trade varieties. Chromium-bearing tourmaline (vivid green) and bi-colour crystals (e.g., watermelon tourmaline — red-pink core, green rim) are prized for their unique character. Paraíba tourmaline from Paraíba state, Brazil (discovered 1987), coloured by copper (Cu²⁺) and manganese, produces neon electric blue-green colours unique in the gem world. Mozambique and Nigeria also produce copper-bearing tourmaline marketed as Paraíba-type, though Brazilian origin commands the highest premiums.
Zodiac Connection: Libra
October birthstones align with Libra (the scales), governing approximately September 23 to October 22. Libra is an air sign associated with balance, harmony, beauty, justice, and the weighing of opposites — governed by Venus, the planet of aesthetics and relationships. October's two birthstones embody Libra's character in complementary ways: opal, which holds all colours simultaneously within its play-of-colour, represents the balancing and harmonising of the full spectrum — a single stone that encompasses everything. Tourmaline, which spans the full colour range and can show multiple colours in a single crystal (watermelon), similarly refuses to choose one extreme, embodying Libra's instinct to see and honour all sides. Venus-ruled Libra's love of beauty finds expression in both gems: opal's fire is among the most spectacular visual phenomena in the mineral world, and tourmaline's variety ensures that any aesthetic preference is met.
Sources & further reading (3)
- gemological-institute — accessed 2026-05-08
- gemological-institute — accessed 2026-05-08
- encyclopedia — accessed 2026-05-08
Frequently asked questions
Is it bad luck for non-October people to wear opal?
This superstition — that opal brings bad luck to those not born in October — appears to derive from a single literary source: Sir Walter Scott's novel 'Anne of Geierstein' (1829), in which an opal amulet is central to a tragic narrative. After the novel's publication, opal sales reportedly declined in Europe. There is no gemological or cultural basis for the superstition prior to Scott's novel, and it is contradicted by centuries of positive opal symbolism across Roman, Arab, and indigenous Australian traditions. The ancient Romans called opal 'opalus' and considered it a stone of hope and good fortune. Australian Aboriginal traditions, in cultures from which Australia's opals originate, associate opal with creator ancestors and sacred significance. The bad-luck association is a 19th-century literary creation that was subsequently amplified by diamond trade marketing in the 20th century to promote diamond over opal competitors.
What is a doublet or triplet opal?
Opal doublets and triplets are assembled gems that simulate precious opal using thin slices of opal layered with backing and/or capping materials. A doublet consists of a thin layer of precious opal (too thin to be set alone) cemented to a dark backing (ironstone, black potch opal, or black glass) that simulates the dark body colour of black opal. A triplet adds a transparent quartz or glass dome over the top, improving protection and magnifying the play-of-colour appearance. Doublets and triplets are legitimate and commercially widespread, but must be disclosed as assembled stones, not solid opal. They are significantly less expensive than equivalent solid black or boulder opal. Identification: doublets and triplets look unnaturally perfect in play-of-colour and show a distinct junction line under magnification at the girdle. Water can penetrate the adhesive layer over time in doublets, causing cloudiness.
Is Paraíba tourmaline more valuable than other tourmalines?
Yes, significantly. Paraíba tourmaline — defined by the presence of copper as a chromophore producing neon electric blue-green colours — commands extraordinary premiums over other tourmaline varieties. Fine one-carat Brazilian Paraíba tourmaline can retail for $20,000–$50,000 per carat; exceptional specimens in larger sizes have sold for $100,000+ per carat at auction. By comparison, fine rubellite (red tourmaline) might retail for $500–$5,000 per carat, and standard green tourmaline for $50–$500. The premium reflects the unique colour (no other gem produces the saturated neon blue-green of copper-bearing tourmaline), rarity (the original Paraíba deposit in Brazil is nearly exhausted), and the high demand from collectors. GIA laboratory reports specifically identify copper content as the defining criterion for 'Paraíba type' designation; origin (Brazil vs. Mozambique/Nigeria) further affects price, with Brazilian stones commanding the highest premiums.