Is quartz really that common?

Yes. Silicon and oxygen are the two most abundant elements in the crust, and quartz is roughly twelve per cent of it by volume. That abundance is why quartz varieties dominate any crystal shop and why they are cheap, which is a good thing: it means the most-used stones in the tradition are within anyone's reach.

Why do emerald and aquamarine cost such different amounts?

Same mineral, different scarcity and different flaws. Emerald owes its green to chromium or vanadium, which arrive through geological conditions that also fracture the crystal, so almost every emerald is included and oiled. Aquamarine grows cleaner and larger. Price follows clarity and size far more than it follows the species.

What is a trade name and why does it matter?

A name invented to sell a stone rather than to describe it. Some are harmless shorthand, some are actively misleading, and a few describe material that does not exist as a natural mineral at all. The rule of thumb: if a name has no entry in a mineralogical database, ask what the underlying mineral is before you pay.

Does family membership change a stone's meaning?

In practice people treat family members as relatives with distinct characters, which is a reasonable way to work. It is worth noticing that the differences you feel between amethyst and citrine are differences of colour and association rather than of substance, since both are quartz. Whether that matters is a question the tradition has never settled.

Which family is the most dangerous to handle?

The carbonates and the copper-bearing greenstones, because malachite, azurite and chrysocolla release copper as dust or in water. Beyond that, watch pyrite, which can produce sulfuric acid as it decays, some serpentine, which carries asbestos fibres, and anything containing lead or mercury. Cutting and grinding is where the real risk lies; a polished piece on a shelf is inert.

The mineral families

Twelve mineral families

The chemistry underneath the folklore. Grouping stones by what they are rather than by how they look explains why amethyst and citrine are the same mineral, why emerald and aquamarine are the same mineral, and why a stone at hardness 3 should never go in a daily ring.

12: families
60: stones placed
2–10: Mohs range

The twelve families

Each family page gives the chemistry, the members in this catalogue, the trade names to watch and the care rules that follow from the structure.

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Quartz

8 stones SiO₂, trigonal

The most abundant mineral family in the crust and the backbone of every crystal shop. One substance, a dozen trade names, separated by trace iron, radiation damage and inclusions.

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Chalcedony & jasper

7 stones SiO₂, cryptocrystalline

Quartz grown too fine to see, in fibres or grains. This is where banding, patterning and the whole world of carved seals and cameos comes from.

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Beryl

3 stones Be₃Al₂Si₆O₁₈, hexagonal

One mineral wearing four famous names. Emerald, aquamarine, morganite and heliodor differ only in which trace metal coloured the crystal.

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Corundum

2 stones Al₂O₃, trigonal

Hardness 9, second only to diamond. Red corundum is ruby, every other colour is sapphire, and that naming split is a matter of trade rather than chemistry.

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Feldspar & the feldspathoids

6 stones framework aluminosilicates

Sixty per cent of the crust, and the source of the flash stones. Moonstone and labradorite shimmer because of layering inside the crystal, not because of anything added.

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The gem silicates

6 stones assorted silicates

Garnet, peridot, topaz, iolite, tanzanite and kunzite. Chemically unrelated, grouped here because they are the classic faceted stones of the jeweller's tray.

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Tourmaline & the layered silicates

4 stones borosilicates & micas

Tourmaline is the most chemically complicated common gem; the micas and kyanite share its habit of growing in sheets and blades.

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The carbonates

5 stones CO₃ minerals

Malachite, azurite, rhodochrosite and calcite. Soft, often vividly coloured, frequently copper-bearing, and all of them dissolved by acid.

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Evaporites & halides

3 stones sulfates & halides

Selenite, celestite and fluorite. Stones that crystallised out of drying water, which is why several of them will dissolve if you put them back in it.

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The metallic ores

3 stones oxides & sulfides

Hematite, pyrite and lodestone. Heavy, metallic, magnetic or shining, and the group whose observable behaviour generated the most folklore.

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Greenstones & copper minerals

5 stones assorted

Jade, turquoise, chrysocolla, larimar and apatite. Grouped by how they were used rather than by chemistry, because whole civilisations organised around exactly this colour.

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Carbons, glasses & organics

8 stones non-silicate & non-mineral

Diamond, shungite, obsidian, moldavite, opal, amber, jet and pearl. What the catalogue holds that is not a conventional crystal at all.

What a family tells you that a colour cannot

Grouping stones by chemistry is a modern habit, and it is the single most useful correction to the older way of working. Three things follow from it directly.

The first is identity. Amethyst, citrine, smoky quartz, rose quartz, tiger's eye, agate, carnelian, onyx, jasper and bloodstone are all silicon dioxide. They differ in trace iron, in radiation damage, in the size of the crystals and in what got trapped inside while they grew. A practice that assigns ten sharply distinct meanings to ten faces of one mineral is telling you about human perception rather than about matter, which is worth knowing while you use it.

The second is care. Structure predicts behaviour. Sulfates and halides crystallised out of drying water, so selenite dissolves and celestite crumbles. Carbonates fizz in acid, so malachite and rhodochrosite should never meet vinegar or a swimming pool. Sulfides oxidise, so pyrite decays in a humid room. None of this is mystical and all of it is preventable.

The third is honesty in the shop. Once you know that beryl covers emerald, aquamarine and morganite, you understand why a pale emerald and a deep aquamarine can look confusingly alike. Once you know that most bright citrine is heated amethyst and most blue topaz is irradiated, you stop paying rare-stone prices for common material.

How these twelve were drawn

Six of the families are real mineralogical groups: quartz, chalcedony, beryl, corundum, feldspar and the carbonates. Three are practical groupings by shared behaviour rather than by strict classification: the evaporites, the metallic ores, and tourmaline with the layered silicates. Three are groupings by how the stones were actually used: the gem silicates of the jeweller's tray, the greenstones and copper minerals that whole civilisations organised around, and the carbons, glasses and organics that are not conventional crystals at all.

Where a placement is a judgement call, the family page says so and gives the true chemistry. Nothing is hidden to keep the scheme tidy.

Frequently asked questions

: Yes. Silicon and oxygen are the two most abundant elements in the crust, and quartz is roughly twelve per cent of it by volume. That abundance is why quartz varieties dominate any crystal shop and why they are cheap, which is a good thing: it means the most-used stones in the tradition are within anyone's reach.
: Same mineral, different scarcity and different flaws. Emerald owes its green to chromium or vanadium, which arrive through geological conditions that also fracture the crystal, so almost every emerald is included and oiled. Aquamarine grows cleaner and larger. Price follows clarity and size far more than it follows the species.
: A name invented to sell a stone rather than to describe it. Some are harmless shorthand, some are actively misleading, and a few describe material that does not exist as a natural mineral at all. The rule of thumb: if a name has no entry in a mineralogical database, ask what the underlying mineral is before you pay.
: In practice people treat family members as relatives with distinct characters, which is a reasonable way to work. It is worth noticing that the differences you feel between amethyst and citrine are differences of colour and association rather than of substance, since both are quartz. Whether that matters is a question the tradition has never settled.
: The carbonates and the copper-bearing greenstones, because malachite, azurite and chrysocolla release copper as dust or in water. Beyond that, watch pyrite, which can produce sulfuric acid as it decays, some serpentine, which carries asbestos fibres, and anything containing lead or mercury. Cutting and grinding is where the real risk lies; a polished piece on a shelf is inert.

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