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Gem Education
Everything you need to know about gemstones — from understanding quality factors to choosing the perfect stone. Brought to you by Melbourne's trusted gem experts.
The 4Cs of Gemstone Quality
Just like diamonds, coloured gemstones are evaluated based on four key characteristics. Understanding these will help you make informed decisions when selecting a gemstone.
Colour
The most important factor for coloured gemstones. Colour is assessed by three attributes: hue (the actual colour), saturation (the intensity), and tone (the lightness or darkness). The most valuable stones exhibit vivid, evenly distributed colour.
Clarity
Clarity refers to the presence of internal inclusions or external blemishes. While some gemstones like emeralds are expected to have inclusions, others like aquamarine are prized for their transparency. Each gemstone type has its own clarity standards.
Cut
The cut of a gemstone affects how it interacts with light. A well-cut stone will exhibit brilliance, fire, and scintillation. Common cuts include oval, round, cushion, emerald, pear, and marquise. The quality of the cut influences both beauty and value.
Carat Weight
Carat is the unit of weight for gemstones, where one carat equals 0.2 grams. Larger stones are rarer and more valuable, but size alone doesn't determine worth — a smaller stone with excellent colour and clarity can be more valuable than a larger stone of lesser quality.
Popular Gemstone Types
Sapphire
Best known for their rich blue colour, sapphires actually come in every colour except red. They are one of the hardest gemstones (9 on the Mohs scale), making them excellent for everyday wear. Notable origins include Sri Lanka, Myanmar, and Kashmir.
Ruby
Rubies are red varieties of the mineral corundum, the same family as sapphires. The most prized colour is "pigeon blood" red — a vivid, slightly purplish red. Rubies are among the most valuable coloured gemstones in the world.
Emerald
Valued for their lush green colour, emeralds are a variety of the mineral beryl. Unlike many gemstones, inclusions in emeralds (called "jardin") are expected and can even add character. The finest emeralds come from Colombia, Zambia, and Brazil.
Spinel
Once confused with rubies and sapphires, spinel has gained recognition as a desirable gemstone in its own right. Available in a range of colours from vivid red to cobalt blue, spinels offer excellent brilliance and durability at an attractive price point.
Alexandrite
Famous for its remarkable colour-change effect — appearing green in daylight and red under incandescent light. Alexandrite is one of the rarest and most prized gemstones, belonging to the chrysoberyl mineral family.
Gemstone Treatments
Many gemstones undergo treatments to enhance their appearance. At Mustard Seeds Gems, we always disclose any known treatments. Common treatments include:
- Heat Treatment — The most common enhancement, used to improve colour and clarity in sapphires and rubies. Widely accepted in the industry.
- Oil/Resin Treatment — Commonly used in emeralds to fill surface-reaching fractures and improve clarity.
- No Treatment — Untreated stones are rarer and typically command higher prices. We clearly label untreated gemstones in our collection.
Tips for Choosing a Gemstone
1. Decide on your purpose. Are you buying for jewellery, investment, or a collection? This influences which qualities matter most.
2. Prioritise colour. For coloured gemstones, colour is the most important value factor. Choose a colour that appeals to you personally.
3. Set a budget. Beautiful gemstones exist at every price point. A well-chosen stone within your budget is better than an overstretched purchase.
4. Ask questions. Don't hesitate to ask about origin, treatments, and certifications. A reputable seller will always be transparent.
5. Buy what you love. At the end of the day, the best gemstone is the one that speaks to you. Trust your eye and your instinct.
Ready to find your gemstone?
Browse our collection or reach out for personalised guidance from our team.