Prasiolite

Prasiolite is a green variety of quartz that owes its colour to ‘impurities’ – elements that have found their way into the crystal lattice of the quartz. In prasiolite, the colour is caused by iron atoms incorporated in or between the crystal lattice, in combination with natural radiation.

There are only a few places in the world where natural prasiolite is found. The best known are Silesia (Poland), Montezuma (Brazil), Farm Rooisand (Namibia) and Thunder Bay (Canada).

However, most of the prasiolite seen on the market is not natural prasiolite but heat-treated amethyst. The chemical composition of amethyst and prasiolite is very similar, and these two quartz varieties often occur together at the locations mentioned above. We are familiar with the heating of amethyst from so-called ‘burnt amethyst citrine’, but some amethyst turns green when heated at a lower temperature.

Natural prasiolite is very pale green (Brazil, Thunder Bay) or brownish green to almost brown (Poland). The natural variety is extremely rare and is only rarely offered for sale. You may therefore assume that the vast majority of prasiolite in shops is the heat-treated amethyst variety (including faceted stones). Sometimes you will also see ‘prasiolite’ tumbled stones showing the banding of chevron amethyst; this is because they were originally chevron amethyst and are not natural prasiolite. The so-called ‘amegreen’, a combination of green ‘prasiolite’ and purple amethyst, has also been helped along by human intervention and artificially heated.

Prasiolite is sometimes referred to as ‘green amethyst’. The name is somewhat understandable if you consider that both varieties owe their colour to iron and, in very rare cases, may occur together. Nevertheless, it is a misleading term. Most natural prasiolite has never been amethyst. And virtually all ‘green amethyst’ on the market is not prasiolite. You will most commonly see this green ‘amethyst’ as a variant of the so-called ‘Galaxy’ or ‘Rainbow amethyst’. Let us be clear about one thing… green amethyst does not exist. According to the official definition, amethyst is the purple variety of the mineral quartz in its macrocrystalline form.

‘Green amethyst’ is either quartz that appears green due to a green matrix or included mineral, or it is a trade name for man-made prasiolite – amethyst that has been turned green by heating. In the first case, it is not amethyst, and in the second case, it is not natural. In both cases, therefore, the name is incorrect.