A name is not always a species

A gemstone label can answer several questions at once, but its words do different jobs. Mineral species identifies a material through its chemistry and crystal structure. Variety names distinguish familiar appearances within a species. A mineral group gathers related species. These are useful levels of description, rather than a league table of desirability.

Begin by asking what kind of name you have encountered. Ruby is a variety; corundum is its mineral species. Garnet names a group. A colour word such as green describes an appearance shared by many unrelated materials. Understanding those differences makes a collection easier to explore without mistaking resemblance for identity.

Evidence: Natural History Museum: Describing a new mineral species, GIA: ruby description, GIA: garnet description

Worked example: ruby and sapphire

Place a red ruby beside a blue sapphire in your imagination. The colour contrast is dramatic, yet both belong to corundum. Chromium produces ruby's red; iron and titanium can produce blue in sapphire. Small chemical differences can therefore matter greatly to what the eye sees without requiring a new mineral species.

Sapphire also includes pink, yellow, green and other colours, as well as colourless material. It is not simply a scientific word for blue. When a label reads yellow sapphire, the first word describes colour and the second identifies a corundum variety. A yellow stone of another species does not become sapphire because its hue matches.

Evidence: GIA: ruby description, GIA: Sapphire description

Worked example: one species, different experiences

Aquamarine and emerald are varieties of beryl. Aquamarine's familiar blue to greenish blue differs from emerald's green to bluish green, but their shared species is a more meaningful relationship than colour resemblance to an unrelated gem.

Do not carry the comparison too far. Species membership alone does not tell you a particular stone's condition, inclusions or treatment history. Think of the species as the first line in a record, not the completed record. Two beryls can deserve different handling or further examination. The helpful next question is what is known about this specimen, rather than what is usually true of the family.

Evidence: GIA: Aquamarine description

A group can contain many species

Garnet offers a different pattern. Its members have related crystal structures but differing compositions. Familiar gem species include pyrope, almandine, spessartine, grossular and andradite. Many individual garnets combine components associated with more than one species. A tidy chart is an introduction to that chemistry, not a promise that every specimen occupies an isolated box.

Tourmaline is also a group with multiple species and many colours. A pink tourmaline and a green tourmaline are not automatically different mineral species. Equally, a colour-based variety or trade name should not be used as a substitute for an actual chemical identification.

Evidence: GIA: garnet description, GIA: Tourmaline description

Colour and shape belong in separate fields

Try reading an imaginary label: blue sapphire, oval cabochon. Sapphire supplies material information, blue supplies a colour description, oval supplies the outline, and cabochon describes a rounded polished form without an ordinary faceted crown. Those words can coexist because they answer different questions.

Some corundum contains oriented inclusions that can produce a star across a suitably cut cabochon. The cutter's orientation helps reveal that effect; the star is not a separate mineral species. Similarly, cutting a stone into a familiar outline cannot establish its material identity. A photograph may illustrate colour, outline or a visible phenomenon while leaving the identification unverified.

Evidence: GIA: Sapphire description

Make a useful collection label

For a learning notebook, use separate fields for the supplied name, proposed species or group, observed colour, cutting style and evidence. Add natural or laboratory-grown status and treatment information only when supported. Write unknown when the record does not answer a question. This keeps an attractive descriptive name from silently becoming a laboratory conclusion.

Do the same when two sources use different labels. Record the wording before deciding whether they disagree. One may name a broad group while the other names a variety within it. Precision begins with understanding the level of the claim, not choosing whichever name sounds more impressive.

Evidence: Natural History Museum: Describing a new mineral species, GIA: garnet description

Self-check: what does each name tell you?

Question one: are ruby and blue sapphire different mineral species? No. They are different corundum varieties. Question two: does green identify one particular gem? No. It is a colour description that can apply to unrelated materials. Question three: does garnet identify one fixed composition? No. It describes a group, and many garnets have mixed compositions.

Now choose any two entries in this collection. Write one sentence about their mineral relationship and another about their visible appearance. Keep the sentences separate. If the first answer is uncertain, follow the entry's identification source rather than guessing from its image.

Evidence: GIA: ruby description, GIA: garnet description, GIA: Sapphire description