From colour and beauty to rarity and durability, we deep dive into the qualities that give coloured gemstones their coveted value and undeniable appeal.

Subjected to immense heat and pressure deep beneath the Earth’s surface, minerals and organic material are transformed into otherworldly crystalline structures over millions of years. This is the incredible journey of a gemstone. It endures the shifting of continents, the eruption of volcanoes and the slow carving of rivers and mountains.

At SARAH & SEBASTIAN, gemstones are often the beating heart of our collections, with Creative Director and Gemologist Sarah Gittoes designing pieces around a chosen coloured stone. Our latest AURELIA collection champions natural Australian opals, while our PILLAR pieces shine a light on emeralds and tourmalines.

Exploring the prismatic world of coloured gemstones, we uncover the qualities and properties that give them an enduring appeal, with expert insights from our in-house gemologist and gemstone sourcing specialist, Crissabella.

The Gemstone Trifecta: Three Key Elements That Define Its Value

BEAUTY

“Beauty will always be the first thing a person thinks of when you say ‘gemstone’, which usually refers to its hue, saturation and tone of colour,” says Crissabella. “But there are two other key factors that give a gemstone its value and enduring appeal: beauty, durability and rarity—this is the holy trinity. The more a gemstone excels in all three of these aspects, the more valuable it is.”

DURABILITY

“Durability refers to its hardness, toughness and stability,” explains Crissabella. “This is crucial in determining how well it can withstand daily wear and time when it comes to jewellery. For example, jade is incredibly tough and nearly impossible to break, which means they will endure when worn daily.”

Sapphires and diamonds are extremely durable gemstones, scoring nine and ten, respectively, on the MOHs hardness scale, making them ideal for bridal pieces as they will stand the test of time. This globally recognised scale measures a gemstone’s resistance to scratching, fracturing or cleaving. “Ideally, engagement rings, wedding bands or heirloom jewellery should only feature gemstones with an MOH hardness between eight and ten,” adds Crissabella.

RARITY

“Rarity refers to how common it is to obtain the gemstone. Contrary to popular belief, white diamonds are rather easy to source, while a gemstone like red beryl (the emerald family) is incredibly rare to find,” Crissabella reveals. “To put this into perspective, for every single red beryl crystal, you'll find roughly 150,000 white diamonds.”

While the four C’s—cut, carat, colour and clarity—play a critical role in determining the value of a gemstone, generally speaking, the rarer it is the more valuable it tends to be.

Emeralds, Sapphires & Rubies: The Royal Trio Of The Gemstone World

Widely regarded as the royal trio, emeralds, sapphires, and rubies stand as the most precious and sought-after coloured gemstones, long symbolising power, prestige and luxury. Their rarity in high-quality forms, unmatched colour intensity, and impressive hardness—ranking eight and nine respectively on the MOHs scale—give them the coveted trifecta of beauty, durability and scarcity. This combination cements their status as some of the most valuable gemstones in the world.

OPAL: Kaleidoscopic Hues & One-Of-A-Kind Patterns

“The reason why precious opals are so mesmerising is because they exhibit a sheen called play-of-colour,” explains Crissabella. “This refers to the reflection and diffraction of light off very small silica spheres that make up the internal structure of the opal, creating a stunning kaleidoscope of patterns and colours.”

This is especially true for black opals, some of the world’s rarest and most sought-after varieties, found in a small opal town called Lightning Ridge in Australia’s rural New South Wales. This is where Creative Director Sarah Munro hand-selected black opals for six one-of-a-kind pieces for our latest AURELIA collection.

“The Opalus Bracelet from AURELIA is truly one of the most exquisite pieces of jewellery I've encountered,” continues Crissabella. “It offers a unique take on the classic tennis design, with Coober Pedy opals displaying a stunning play-of-colour in a range of hues, adding a touch of magic to its beauty.”

TOURMALINE: The Spectral Gemstone

Tourmaline is one of the most diverse gemstones when it comes to its tonal range, occurring in almost every shade of the colour spectrum, from translucent greens to bi-coloured pinks and blues. Compared to diamonds, sapphires and emeralds, tourmalines are a more affordable choice.

“Our Tourmaline Pillar Ring from our PILLAR collection is a gorgeous piece of jewellery,” Crissabella muses. “I love that it’s a bigger ring with a Nigerian tourmaline that is beautifully custom-cut to highlight its natural geometric shape and stunning deep forest green colour.”

EMERALD: The Glowing Gemstone

Unlike most other coloured gemstones, emeralds don’t emit a sparkle, they glow, emanating a rich, striking green hue. With many of the finest stones coming from Columbia, they are prized for their rarity and were historically treasured by Egyptian pharaohs, Mughal emperors, and European royalty.

“Emeralds usually contain natural inclusions, known as jardin (French for ‘garden’),” explains Chrissabella. “While this is often an unfavourable trait in other gemstones, they add to the character and rarity of emeralds rather than diminishing their value.”

At SARAH & SEBASTIAN, emeralds have featured heavily across our signature and seasonal collections: our Divers Earrings, accented by two vivid green Zambian emeralds, epitomise understated modern luxury, while our Emerald Cluster Earrings are the perfect intricate studs to elevate any Ear Alchemy styling.

PEARL: The Ocean’s Natural Treasure

Unlike gemstones that form deep within the Earth, pearls are born from the sea. “Pearls naturally occur within the soft tissue of oysters and molluscs, developing when a minute irritant, such as organic debris, enters the creature’s shell,” explains Crissabella. “As a defence mechanism, it secretes nacre that coats the irritant in layers—the same luminous substance that creates its signature pearlescent finish—gradually resulting in a solid pearl.”

While most rough gemstones require faceting to bring out their shine, pearls don’t need cutting or polishing. Their spherical or idiosyncratic shapes are naturally occurring, making them truly unique.

Celebrated for their classic elegance, pearls have always been a timeless jewellery staple. At SARAH & SEBASTIAN, pearls are often the subject of our most creative designs. Featuring irregular, natural Keshi pearls, our Fine Kelp Pearl Earrings are a bold statement pair, wrapped in a fluid setting. For a minimalist approach, our Venus Pearl Chain is dotted with petite seed pearls, offering understated sophistication.

Discover SARAH & SEBASTIAN’s collection of coloured gemstone jewellery here.