Gemstones have captivated humanity for thousands of years, prized for their colour, rarity, and the sense of wonder they inspire. Whether you are choosing a gemstone engagement ring, selecting a meaningful gift, or simply curious about what sets a ruby apart from a sapphire, understanding the key types of gemstones and what makes each one special is a genuinely rewarding starting point. This guide covers the most important gemstones, how they are evaluated, and how to choose the right one for your jewellery.
Key Takeaways
- Gemstones are traditionally divided into precious (diamonds, rubies, sapphires, emeralds) and semi-precious stones (amethyst, topaz, peridot), though this distinction has become less rigid over time.
- A gemstone's value is assessed across five dimensions: colour, clarity, cut, carat weight, and hardness on the Mohs scale.
- Diamonds are the hardest natural substance, rating 10 on the Mohs scale, and are the most prized of all precious gemstones.
- Sapphires and rubies are both exceptionally durable (Mohs 9) and well-suited to everyday jewellery including engagement rings and wedding bands.
- Emeralds are softer and better suited to occasional wear, but are among the most coveted coloured gemstones for their depth of colour.
- Semi-precious stones like amethyst, topaz, and peridot offer vibrant colour at more accessible price points.
Understanding Gemstones
Precious vs Semi-Precious Gemstones
Gemstones are traditionally divided into two categories: precious and semi-precious. Precious gemstones, diamonds, sapphires, emeralds, and rubies, are distinguished by their exceptional rarity, brilliance, and durability. Historically, they have adorned the jewellery of royalty and served as symbols of wealth, status, and power across cultures worldwide.
Semi-precious gemstones, such as amethyst, topaz, and peridot, are generally more abundant and more affordable while remaining deeply beautiful and widely beloved. In recent years, however, the boundary between the two categories has become less rigid, many semi-precious stones are now highly sought after and command significant prices when they display exceptional colour or clarity.
How Gemstones Are Evaluated: The 4Cs and Hardness
A gemstone's value is assessed across five key dimensions, the same 4Cs used for diamonds, plus one additional factor unique to gemstones:
Colour: The most important factor for most coloured gemstones. Evaluated across three dimensions: hue (the actual colour), saturation (intensity of the colour), and tone (lightness to darkness). The ideal colour differs by gemstone type, rubies are prized for vivid red, sapphires for deep blue, emeralds for rich green.
Clarity: The absence of internal inclusions or surface blemishes. Clearer stones are rarer and more valuable, though some gemstones (notably emeralds) are almost always included, and inclusions are considered part of their natural character.
Cut: How well the stone has been shaped and faceted. A good cut maximises the gem's brilliance and colour display; a poor cut can make even a fine stone appear dull.
Carat weight: The measure of the gemstone's weight. Larger stones of fine quality are exponentially rarer and more valuable than smaller ones.
Hardness (Mohs Scale): Hardness measures a gemstone's resistance to scratching and abrasion, which directly affects its suitability for different jewellery types and how well it holds up to daily wear. The Mohs scale runs from 1 (softest) to 10 (hardest). A diamond, rated 10, can only be scratched by another diamond. Gemstones rated 7 and above are generally suitable for rings and other pieces that receive daily contact; softer stones are better suited to earrings, pendants, and pieces with less exposure.
Precious Gemstones
Diamond
Diamond is the hardest natural substance on Earth, rating 10 on the Mohs scale — the only gemstone that can scratch all others. Formed deep within the Earth under extreme heat and pressure, diamonds are prized above all other gemstones for their extraordinary brilliance, fire, and durability. A well-cut diamond refracts light in a way no other stone can replicate, producing the unmistakable sparkle that has made it the world's most coveted gem.
Diamond quality is assessed using the 4Cs: Cut, Colour, Clarity, and Carat, with cut being the single most impactful factor on a diamond's visual appearance. Colourless diamonds (graded D to F) are the rarest; most buyers find excellent value in the G to I range. For certified diamond jewellery with the highest quality assurance, explore Poh Heng Trust® Diamonds — independently certified pieces backed by a lifetime trade-in privilege. Browse our full diamond jewellery collection for rings, pendants, earrings, and more.
Sapphire
Sapphire is a precious gemstone prized for its striking colour and exceptional durability, rating 9 on the Mohs scale, second only to diamond. While the name derives from the Greek sappheiros meaning blue stone, sapphires are found in nearly every colour of the rainbow, including pink, yellow, white, and the rare and prized Padparadscha (orange-pink). Blue sapphires remain the most iconic, with the finest stones displaying a vivid, medium-dark blue with strong saturation.
A sapphire's cut significantly influences its colour: a shallower cut increases light entry and brightness, while a deeper cut intensifies colour saturation. Their hardness makes sapphires ideal for engagement rings and everyday jewellery, they will retain their surface polish and resist scratching over decades of wear. Explore Poh Heng's sapphire jewellery collection for pieces crafted in this exceptional stone.
Emerald
Emerald is one of the most coveted coloured gemstones in the world, known for its rich, distinctive green that ranges from light yellow-green to a deep, velvety dark green. The finest emeralds display an intense, evenly distributed green with strong saturation, a depth of colour that no other gemstone fully replicates.
Emeralds have a hardness of 7.5–8 on the Mohs scale, making them somewhat softer than sapphires and rubies. They are also almost universally included, natural fractures and inclusions are so characteristic of emeralds that the French term jardin (garden) is used to describe them, and they are considered part of the stone's natural identity rather than flaws. The most valuable emeralds, however, are eye-clean with no inclusions visible to the naked eye. Due to their relative softness, emeralds are best suited to occasional-wear jewellery or protective settings such as bezels.
Ruby
Ruby is famed for its deep, fiery red, one of the most emotionally powerful colours in all of gemology. Its name comes from the Latin ruber, meaning red, and its colour ranges from a warm pinkish red to a vivid, slightly purplish red. The most prized rubies display an intense, medium-dark red, sometimes described as "pigeon's blood", a pure, vivid red with a hint of blue.
Like sapphires, rubies rate 9 on the Mohs scale, making them extraordinarily durable and highly suited to all types of jewellery, including rings and pieces worn daily. Colour is the dominant factor in a ruby's value: evenness of colour distribution, saturation intensity, and the absence of brownish or orangey overtones all contribute to a stone's desirability. Explore our ruby jewellery collection for pieces set in this vibrant, passionate gemstone. For other beautifully coloured gemstone options, browse our full coloured gemstone collection.
Semi-Precious Gemstones
Amethyst
Amethyst is a striking purple variety of quartz and one of the most popular and versatile semi-precious gemstones. Its colour ranges from a delicate pale lavender to a deep, rich violet, the finest stones displaying a vivid, strongly saturated purple without brown or bronze overtones. Amethyst rates 7 on the Mohs scale, making it durable enough for regular wear in most jewellery types, though it is best avoided during rough physical activity.
Its relative affordability compared to precious gemstones makes amethyst an excellent choice for those who love vibrant colour without a significant premium. It has long been associated with qualities of calm, clarity, and wisdom.
Topaz
Topaz is found in a wide range of colours, blue, yellow, pink, orange, and colourless — making it one of the most versatile gemstones available. The most widely recognised colour is blue, often achieved through treatment, with sky blue and London blue being the most popular varieties. Imperial topaz, in a rich orange-yellow, is the rarest and most valuable form.
With a hardness of 8 on the Mohs scale, topaz is an excellent choice for everyday jewellery. Its value is determined primarily by colour and clarity, with well-cut stones showcasing exceptional brilliance.
Peridot
Peridot is an olive to lime green gemstone with an instantly recognisable colour, unlike virtually every other gemstone, peridot's green is not caused by trace impurities but by the presence of iron within its fundamental mineral structure.
This gives it a uniquely natural, warm glow. It rates 6.5 to 7 on the Mohs scale, making it somewhat more susceptible to scratching than harder gems; it is best suited to earrings and pendants rather than rings that receive daily abrasion.
The most desirable peridots display a rich, vivid green with no visible inclusions.
Pearls: A Special Case
Pearls occupy a unique position in the world of gemstones, they are the only gem produced by a living creature, formed when an oyster or mollusc coats an irritant with successive layers of nacre. Unlike mineral gemstones, pearls require no cutting or faceting; their beauty is entirely natural. They come in a range of colours including white, cream, pink, and black, and are prized for their lustrous, glowing surface.
Pearls are a softer gem (Mohs 2.5–4.5) and should be stored separately and kept away from perfumes, cosmetics, and acids to preserve their lustre. Explore our pearl jewellery collection or read our dedicated pearls guide for more on selecting and caring for pearl jewellery.
Rarity, Natural vs Synthetic Gemstones
Rarity and Value
Beyond the 4Cs and hardness, a gemstone's rarity is one of the most powerful determinants of its value. Diamonds, rubies, sapphires, and emeralds of exceptional quality are genuinely scarce, fine specimens of a single carat can be extraordinarily difficult to source. Semi-precious stones, while more abundant, can also achieve significant value when they display exceptional colour, clarity, or size.
Natural vs Synthetic Gems
Natural gemstones are formed within the Earth over millions of years through geological processes; their rarity and natural origin are core to their value and appeal. Synthetic (or lab-grown) gemstones are created in laboratories through processes that replicate the physical, chemical, and optical properties of their natural counterparts. Both types can be visually indistinguishable to the unaided eye, and both have their place.
Natural gemstones carry the premium of rarity and provenance, a quality that matters particularly for meaningful purchases such as engagement rings or anniversary gifts. Synthetic gemstones offer excellent visual quality at more accessible price points and have a lower environmental footprint. The right choice depends on your priorities, budget, and the significance of the piece.
Gemstones in Jewellery
Choosing the Right Gemstone for Each Jewellery Type
Different types of jewellery expose gemstones to very different levels of wear and impact, and choosing a stone with appropriate hardness for the piece is important.
Rings receive the most daily contact and abrasion of any jewellery type. For rings, particularly engagement rings and everyday rings, gemstones rated 7.5 or higher on the Mohs scale are strongly recommended. Diamonds, sapphires, and rubies are all excellent choices.
Necklaces and pendants are less exposed to direct impact and abrasion, making a wider range of gemstones suitable. Browse our necklaces collection for gemstone pendant options.
Earrings are the most forgiving jewellery type for softer stones, even peridot and amethyst work beautifully in earrings, as they face minimal contact risk.
Bracelets fall between rings and necklaces in terms of exposure, medium-hard stones (Mohs 7+) are a sensible choice. Explore our bracelets collection for gemstone bracelet options.
Gemstones in Singapore's Bridal Traditions
In Singapore, coloured gemstones play a meaningful role in bridal jewellery beyond the traditional diamond. The Si Dian Zuan, the diamond equivalent of the traditional Si Dian Jin bridal gift, features diamond-set pieces that carry both cultural significance and lasting value. Explore our Si Dian Zuan collection for beautifully crafted diamond bridal jewellery suited to this cherished tradition.
Closing Thoughts
Beyond their colourful exterior, gemstones are meaningful additions to jewellery and a testament to the extraordinary beauty of the natural world. Whether you are drawn to the intense blue of sapphires, the fiery passion of rubies, or the unique olive glow of peridot, there is a gemstone that speaks to your story.
At Poh Heng, our collections bring together some of the finest coloured gemstones set in beautifully crafted jewellery for every occasion. Explore our Sapphire, Ruby, and Coloured Gems collections online, or visit any of our Poh Heng boutiques to see these stunning pieces in person and find the one that adds a little extra sparkle to your life.
Frequently Asked Questions
What is the difference between precious and semi-precious gemstones?
Precious gemstones, diamonds, rubies, sapphires, and emeralds, are distinguished by their exceptional rarity, hardness, and brilliance. Semi-precious gemstones, such as amethyst, topaz, and peridot, are more abundant but no less beautiful, and often offer vibrant colour at more accessible prices. The distinction has become less absolute in recent years, as some semi-precious stones can command very high prices when they display exceptional quality.
What is the Mohs scale and why does it matter for jewellery?
The Mohs scale is a measure of a gemstone's hardness, specifically, its resistance to scratching. It runs from 1 (softest) to 10 (hardest, for diamond). For jewellery that is worn daily, especially rings, gemstones rated 7 or above are recommended, as softer stones will scratch and lose their polish over time. Earrings and pendants can accommodate softer stones more safely.
Which gemstone is best for an engagement ring?
Diamond is the most popular choice for engagement rings worldwide, owing to its unmatched hardness, brilliance, and enduring symbolism. Sapphires and rubies are excellent alternatives, both rate 9 on the Mohs scale and are exceptionally durable for daily wear. Emeralds, while beautiful, are softer and more fragile and are best suited to protective settings if used in an engagement ring.
What makes a ruby more valuable than other red gemstones?
A ruby's value is determined primarily by its colour — the finest rubies display a vivid, medium-dark red sometimes described as "pigeon's blood". Even colour distribution, strong saturation, and the absence of brownish or orangey overtones all contribute to higher value. Fine rubies are also significantly rarer than many other red gemstones such as garnets or red tourmalines, which contributes substantially to their premium.
Are lab-grown gemstones real?
Yes. Lab-grown gemstones have the same physical, chemical, and optical properties as their natural counterparts, they are not imitations or simulations. The key difference is origin: natural gemstones are formed in the Earth over millions of years, while synthetic stones are created in controlled laboratory environments. Natural stones carry a premium for their rarity and provenance; lab-grown stones offer excellent quality at more accessible prices.
How should I care for my gemstone jewellery?
The care required depends on the gemstone's hardness and composition. Most gemstones can be gently cleaned with warm water, mild soap, and a soft brush. Avoid ultrasonic cleaners for softer or heavily included stones (such as emeralds and pearls). Store pieces separately to prevent harder stones from scratching softer ones. Keep all gemstone jewellery away from harsh chemicals, including household cleaning products and chlorinated water. For professional cleaning and inspection, visit our Jewellery Services at any Poh Heng boutique.