You have seen a green stone and you are looking for its name. Or a blue stone, or a pink one. Online lists line up dozens of minerals in alphabetical order. None of them says which ones survive a ring worn every day. That is the question that matters. This guide sorts stones by colour, then by hardness on the Mohs scale. And it adds a column nobody writes: what that colour gives you as a laboratory-grown diamond.

Precious stone or fine stone: the real French rule

Let's start with the question that comes up everywhere. What are the four precious stones? Diamond, ruby, sapphire and emerald. That is the traditional list, and it is short.

Every other gem is a fine stone, what English usually calls a semi-precious stone. Amethyst, aquamarine, topaz, garnet, tourmaline, peridot, opal. The word takes nothing away. It describes a commercial category, not a quality.

A useful clarification. In France, the gemstone trade regulates the names that may be used. The term "semi-precious stone" has no legal standing there and is no longer used by serious professionals, who say "fine stone" instead. If you read it on a product page, that tells you something about the seller.

Another point the lists forget. This distinction is historical and commercial. It says nothing about strength. A tourmaline, a fine stone, stands up to daily life better than an emerald, a precious stone.

The Mohs scale, the criterion missing from every list

The Mohs scale ranks minerals by their resistance to scratching. It runs from 1, talc, to 10, diamond. Each step scratches the ones below it.

The number that really counts in the life of a jewel is 7. Why 7? Because dust contains quartz, whose hardness is precisely 7. A stone below 7 scratches on contact with ordinary dust. Not from an impact. From dust. Within a few years the surface goes dull.

Here are the markers to memorise. Diamond: 10. Sapphire and ruby, which are two varieties of corundum: 9. Spinel and topaz: 8. Emerald and aquamarine, two beryls: 7.5 to 8. Quartz, including amethyst and citrine: 7. Garnet: 6.5 to 7.5. Peridot: 6.5 to 7. Tanzanite: 6 to 7. Opal: 5.5 to 6.5. Turquoise and lapis lazuli: 5 to 6. Fluorite: 4. Malachite: 3.5 to 4.

An important nuance, often forgotten. Hardness does not say everything. Emerald posts a good hardness but it is fragile, because it is loaded with inclusions and internal fissures. An impact breaks it where a sapphire takes it. Tanzanite and kunzite have clean cleavage planes, which makes them brittle.

Translated into everyday language. For a ring worn permanently, aim for 8 as a minimum. For earrings or a pendant, which take few knocks, 7 is enough. Below 6, keep the stone for occasional pieces.

What is the blue stone called

This is the most asked question on the subject. There is not one blue stone, there are a dozen. Here are the main ones, ranked by fitness for everyday wear.

Sapphire is the reference. Hardness 9, excellent resistance, colour from pale blue to midnight blue. It is the blue stone of classic fine jewellery.

Blue spinel reaches 8. Long confused with sapphire in royal collections, it remains little known to the wider public.

Aquamarine sits between 7.5 and 8. Its blue is pale, almost marine, very luminous. It holds up well day to day.

Blue topaz posts 8. Careful: the blue of topaz is almost always obtained by treatment. Naturally blue topaz is rare. That is not a flaw, but it has to be declared.

Tanzanite, between 6 and 7, offers a unique violet blue. It is fragile and cleaves easily. Keep it for earrings and pendants.

Lapis lazuli and turquoise, between 5 and 6, are opaque stones. They scratch quickly and cope badly with household products.

And as a laboratory-grown diamond? A blue diamond exists and posts a hardness of 10. It is the only blue stone that does not scratch. Where sapphire caps out at 9, blue diamond is untouchable day to day. We compared the two in detail in blue diamond or sapphire.

What is the green stone called

Green is the colour where the names get most tangled. Here is the sorting.

Emerald is the reference green stone. Its hardness is good, between 7.5 and 8, but its resistance to impact is weak. Almost every emerald on the market is oiled to hide its fissures. That oil evaporates over time and care has to be gentle.

Tsavorite is a green garnet, between 7 and 7.5. Its green is vivid and its transparency excellent. It is stronger than an emerald and far less well known.

Green tourmaline, between 7 and 7.5, offers a very wide palette, from olive green to blue green.

Peridot, between 6.5 and 7, gives a characteristic yellow green. It scratches over time on a ring.

Jade actually covers two different minerals, jadeite and nephrite. The toughness of jade is remarkable, its hardness stays moderate.

Malachite and green fluorite are very soft, between 3.5 and 4. Superb as objects, unsuited to a ring.

And as a laboratory-grown diamond? Green diamond exists, at hardness 10. It is the direct alternative to emerald for anyone who wants green without the fragility. Our comparison green diamond or emerald details the gaps.

The names of the pink coloured stones

Pink covers very uneven materials. The difference in strength is more brutal here than in any other colour.

Pink sapphire is a corundum, hardness 9. It is the toughest pink stone after diamond.

Pink spinel, hardness 8, offers vivid pinks and fine transparency.

Morganite is a pink beryl, between 7.5 and 8. Its pink is soft, often peachy. It holds up well.

Pink tourmaline, including the rubellite variety, sits between 7 and 7.5.

Kunzite, between 6.5 and 7, has two weaknesses: it cleaves easily and its colour can fade under prolonged light.

Rose quartz caps out at 7 but stays translucent and milky. Rhodochrosite falls between 3.5 and 4.

And as a laboratory-grown diamond? Pink diamond exists at hardness 10. Let's settle a point of vocabulary, because the confusion is common: a pink stone is set on recycled 18 carat yellow gold, recycled 18 carat white gold, 925 silver or vermeil. The choice of metal changes the look of the pink a great deal. Our article on pink diamonds shows those variations.

Yellow stone: name and solutions

Yellow is the colour served worst by the existing lists.

Yellow sapphire, hardness 9, is the best mineral option. It is little distributed in France, wrongly.

Citrine, hardness 7, is a yellow quartz. It is affordable and often obtained by heating amethyst.

Imperial topaz, hardness 8, leans towards gold and orange. It is the most sought after of the topazes.

Heliodor is the yellow beryl, between 7.5 and 8. Sphene, highly dispersive, does not go past 5.5.

And as a laboratory-grown diamond? Yellow diamond covers the whole range, from soft yellow to deep yellow, at hardness 10. It is the only yellow stone that does not wear.

Transparent and colourless stones

A lot of searches are about the transparent stone with no colour. Here too, several names coexist.

Diamond, hardness 10, is the only colourless stone that combines transparency, fire and strength. White sapphire, hardness 9, is colourless but lacks dispersion, and so lacks fire. White topaz, hardness 8, is a common and cheap imitation. Rock crystal, which is quartz, caps out at 7 and lacks brilliance.

Be careful not to confuse these natural stones with the imitations made to look like diamond. Cubic zirconia and moissanite are not coloured stones, they are substitutes. We treat that subject separately in our article on how to recognise a diamond.

The false trade names to spot

The French nomenclature is full of misleading names. They serve to pass a modest stone off as a prestigious one. Here are a few, with the real name behind each.

"Smoky topaz" is not a topaz. It is smoky quartz, hardness 7. "Bohemian topaz" is a citrine. "Oriental topaz" is a yellow sapphire.

"Green amethyst" does not exist. It is prasiolite, a green quartz obtained by heating amethyst. "Brazilian ruby" is never a ruby: most often it is a pink tourmaline or a pinkish topaz.

The "Herkimer diamond" is quartz, hardness 7. "Water sapphire" is an iolite. "Korean jade" is a serpentine.

The rule is simple. As soon as the name of a prestigious gem is attached to a place name or to an unexpected colour adjective, be suspicious. The real name of a stone fits in one word.

The takeaways

The name of a stone does not tell you whether you will be able to wear it. The Mohs number does. Remember 7 as the low threshold, 8 as the comfortable minimum for an everyday ring.

Every colour has its reference stone. Blue, sapphire. Green, emerald. Pink, pink sapphire. Yellow, yellow sapphire. Each one also has its weak point, fragility, treatment or rarity.

And for each of those colours there is now an option at hardness 10. Our laboratory-grown diamonds cover blue, green, pink and yellow. You can browse the Blue diamonds collection to see what that looks like once set.

To go further. So as not to confuse a real stone with an imitation, read what a fake diamond is called. On yellow, often misunderstood, see the yellow diamond. And to move from the stone to the ring, our article on the setting of a coloured stone shows what the mount changes.

FAQ

What is the green stone called?

There are several. Emerald is the best known. Then come tsavorite, which is a green garnet, green tourmaline, peridot and jade. For everyday wear, tsavorite and tourmaline hold up better than emerald, which is fragile despite its hardness.

What is the dark blue stone called?

Blue sapphire covers the darkest tones, right up to midnight blue. Lapis lazuli gives a deep blue but it is opaque and soft. Tanzanite offers a dark violet blue, with real fragility.

What is the difference between a precious stone and a fine stone?

Only four gems are called precious: diamond, ruby, sapphire and emerald. All the others are fine stones, commonly called semi-precious. It is a commercial and historical classification, with no link to strength and not necessarily to price.

Which coloured stone for a ring worn every day?

Aim for a hardness of at least 8 on the Mohs scale. Sapphire in all its colours, spinel and topaz all work. A coloured laboratory-grown diamond, at hardness 10, is the safest solution.

Why does a stone below 7 on the Mohs scale get damaged?

Because the dust in the air contains quartz, whose hardness is 7. Any softer stone scratches simply from being wiped or rubbed. The wear comes from daily life, not from accidents.

Are there coloured diamonds other than white?

Yes. Blue, green, pink and yellow all exist as laboratory-grown diamonds. The colour comes from elements introduced while the crystal grows, such as boron for blue or nitrogen for yellow. The hardness stays at 10.

Is a "green amethyst" a real amethyst?

No. Amethyst is violet by definition. What the trade calls green amethyst is prasiolite, a green quartz obtained by heating amethyst. The exact name is prasiolite.

Fiona