Paraíba, or a very good blue tourmaline?

The price gap between the two is a factor of a hundred, and almost nothing you can do by eye will close it. Here is what the eye can do, and where it has to stop.

Paraíba is not a mineralogical variety. It is a trade definition agreed between the major laboratories: elbaite tourmaline coloured by copper and manganese, in the blue to blue-green to green range. The definition says nothing about where the stone came from — material from Mozambique and Nigeria qualifies exactly as Brazilian material does — and it says nothing about how good the stone is.

Two consequences follow immediately, and most of the trouble in this market comes from ignoring them. Without copper confirmed by chemical analysis, a stone is not Paraíba, however electric it looks. And copper alone does not make a stone valuable: a pale, washed cuprian elbaite is Paraíba by name and ordinary by every measure that sets a price.

So what can you actually see?

The most useful test costs nothing. Take the stone out of the display lighting and into shade. A fine cuprian tourmaline keeps glowing — the colour appears to come from inside the stone rather than off its surface. An ordinary indicolite or a saturated blue-green tourmaline goes flat and dark in the same conditions. This is not proof of copper, but it separates candidates from wishful thinking faster than anything else.

The reason it works is that copper produces an unusually narrow transmission window. The stone returns one nearly pure colour with very little of the grey component that dulls other gems. That is what people describe as neon, and it survives low light in a way that ordinary saturation does not.

Inclusions help too. Brazilian material is typically heavily included and sometimes contains platelets of native copper — reflective, metallic, and a strong indication of authenticity. Mozambican material tends to be far cleaner and comes in larger sizes; a clean cuprian stone over five carats is almost certainly African rather than Brazilian, whatever the seller prefers to say.

Standard gemmological instruments will not settle it. Tourmaline reads 1.619–1.655 with a birefringence around 0.018 and a specific gravity near 3.06, and those figures are the same for a Paraíba and for an ordinary green tourmaline. What the refractometer does do is eliminate the imitators: neon blue apatite, which looks remarkably similar, has a birefringence of 0.002–0.004 and gives itself away in ten seconds.

The only test that decides the question is a chemical one — EDXRF or LA-ICP-MS, run by a laboratory, looking for copper and manganese. No serious report uses the word Paraíba without it. The same analysis, extended to trace elements, is what allows a laboratory to separate the three sources: gallium, germanium and lead run higher in Nigerian material, magnesium, zinc and antimony in Brazilian.

That origin call matters more here than for almost any other gem, because Brazilian material trades at a multiple of African material of the same appearance. It is also why the origin line on a report is worth more than the stone in some cases.

A last note on treatment. Nearly all cuprian tourmaline is heated at low temperature, which removes the manganese-driven purple component and opens up the blue. The trade accepts this, it is generally not detectable, and it does not damage value. Unheated violet material exists and is a collector's niche. Anyone who tells you their Paraíba is definitely unheated, without a report saying so, is telling you something they cannot know.

Our rule, and we apply it to our own buying: price rough and unreported stones as ordinary tourmaline. Treat a copper confirmation as upside, never as a premise. In a market where the name is worth a hundred times the material, the premise is exactly what gets sold to you.