People usually arrive knowing they want colour and not much beyond that. Which is a fine place to start, because colour is most of the decision.
But not every stone wants to be worn every day. Some are hard enough to survive decades of ordinary life, and some will quietly abrade if you wear them on your hand to do the dishes. Here's what we'd tell you across the bench.
A word about hardness
Gemstones are measured on a scale from one to ten, where diamond sits at ten and talc at one. The scale isn't linear. Diamond is many times harder than the stone immediately below it.
What matters practically is this: anything below about seven and a half will dull over time in a ring worn daily. On earrings or a pendant, which lead gentler lives, the same stone can be perfect.
The hard ones
Sapphire. Nine on the scale, second only to diamond, and our favourite stone to work with. Most people picture the deep blue, but sapphires come in almost every colour: pale cornflower, teal, green, yellow, peach, and the pinkish-orange ones that are among the rarest stones in the world. Untreated, they vary beautifully from one to the next.
Ruby. The same mineral as sapphire, just red. Nine on the scale and extremely durable. The colour to look for is the one that holds under warm indoor light as well as daylight.
Spinel. Eight, and badly underrated. For centuries spinels were mistaken for rubies, including a famous one in the British crown jewels. They come in red, hot pink, grey, lavender and a steely blue-grey we particularly like. Natural, untreated, and still relatively quiet in the market.
Topaz. Eight. Comes in colourless, blue, pink and a warm golden orange. Durable enough for daily wear, though it can chip if struck at the wrong angle.
The middle ground
Emerald. Seven and a half to eight on paper, which sounds safe, but emeralds are full of internal inclusions and that makes them brittle. They need care. Most are also treated with oil to soften the look of those inclusions, and hot water or detergent will strip it. Beautiful, and worth it, but not a stone to forget about.
Aquamarine. The same mineral family as emerald, but clean and pale. Seven and a half to eight, a soft sea blue, and usually free of visible inclusions.
Garnet. Six and a half to seven and a half, and not only the dark red people expect. Garnets come in orange, green, and a raspberry pink.
Tourmaline. Seven to seven and a half. The widest colour range of any gemstone: pink, green, blue, and the watermelon ones that shade from one to the other in a single crystal.
Amethyst. Seven. Purple quartz, from pale lilac to deep grape, and one of the better value coloured stones for its size.
Peridot. Six and a half to seven. A distinctive yellow-green that doesn't look like anything else.
The delicate ones
Opal. Five and a half to six and a half, and porous. Opals hold water inside them and can dry out and craze if treated badly. Extraordinary to look at and best kept to earrings, pendants and rings worn occasionally.
Tanzanite. Six to seven, found in one place on earth, and a violet-blue that shifts depending on the angle you hold it. It also has a natural cleavage plane, which means a sharp knock in the wrong direction can split it. Lovely, but not a daily ring.
Moonstone. Six to six and a half, with that floating blue sheen across the surface. Softer than it looks.
Pearl. Two and a half to four, and organic rather than mineral. Pearls are porous and dislike perfume, hairspray and acid. Wipe them after wearing and store them separately.
Turquoise. Five to six and porous. It can absorb oils from skin and change colour over years, which some people love and some people don't expect.
So which one
If it's a ring you'll wear every day and never take off, we'd point you at sapphire or spinel first. If it's earrings or a pendant, the field is wide open and you can choose purely on colour.
And if you don't know yet, get in touch to discuss. Colour is almost impossible to judge from a photograph, and the stone people leave with is very often not the one they arrived describing.