Know what you are buying
Written from the cutting bench rather than a marketing desk. Each guide covers what actually drives price in that species, which treatments are standard, how the stone behaves in daily wear, and the questions worth asking any seller, including us.
Emerald
Colour saturation drives value far more than clarity. A slightly included stone with vivid, evenly distributed green outperforms a pale, clean one. Swat Valley (Pakistan) emeralds are prized for a cool, slightly bluish green and often show better transparency than Colombian material at the same price point.
Garnet
Garnet is a family, not a single stone. Spessartine (fanta orange), rhodolite (raspberry red-purple) and hessonite (cinnamon orange) are distinct species with different values. Spessartine with true fanta saturation is the most sought after.
Topaz
Sky blue, Swiss blue and London blue describe increasing depth of colour, not different species. Imperial topaz, the natural golden to peach-pink material, is far rarer than any blue topaz and priced accordingly.
Tourmaline
Tourmaline offers the widest colour range of any gem species. Indicolite (blue-teal) and rubellite (true red-pink) carry the strongest premiums. Look for even colour without a dark axis when viewed through the table.
Citrine
Honey and Madeira tones command more than pale lemon. Because large clean crystals are common, citrine is one of the best values in gemstones for statement-sized stones above 10 carats.
Peridot
Peridot is idiochromatic, its green comes from iron in the crystal structure itself, so every stone is green and the only question is tone. The finest is a pure grass green without brown or yellow masking, most often from Pakistan.
Sapphire
Sapphire is corundum in every colour except red. Velvety cornflower blue carries the highest premium, but yellow and purple sapphires offer far more colour per euro and are dramatically under-priced relative to blue.
Ruby
Pigeon blood, a vivid pure red with a faint blue undertone and strong fluorescence, is the benchmark grade. Certification from GUILD, GRS or SSEF matters most above 1 carat, where price per carat rises steeply.
Amethyst
Value sits almost entirely in colour. Deep Siberian purple with red flashes leads; pale or zoned material is abundant and inexpensive. Size adds little premium because large clean amethyst is common.
Corundum
Purple corundum is purple sapphire under a more cautious trade name. The material offers Mohs 9 durability and genuine rarity at a fraction of blue sapphire pricing.
Aquamarine
Unlike emerald, aquamarine is usually eye-clean, so clarity is assumed and colour carries the price. Deeper Santa Maria blue is worth several times a pale sky tone, and larger stones show colour better.
Quartz
Quartz is valued for size, clarity and crystal form rather than rarity. For specimens, an undamaged termination and good matrix presentation matter more than weight.
Ametrine
Virtually all natural ametrine comes from the Anahí mine in Bolivia. Value rests on a crisp, well-centred boundary between purple and gold, and on a cut that presents both colours evenly through the table.
Fluorite
At Mohs 4 fluorite is a display and pendant stone rather than a ring stone. Its appeal is colour banding and the fact that it can be cut in very large sizes with remarkable clarity for a fraction of the cost of any hard gem.
Spinel
Spinel spent centuries misidentified as ruby, several famous crown rubies are spinel. It is singly refractive, brilliant, untreated and still under-priced relative to corundum, making it the connoisseur's value pick.