Journal

Opal, October's birthstone

Guide · · Maedot

Opal is October's birthstone because American jewellers put it there. In August 1912, at a meeting in Kansas City, the retail jewellers' association now called Jewelers of America adopted a list that gave October opal, with tourmaline as the alternate. Most lists in use today still give October both stones.

Who set the list

The gem expert George F. Kunz printed the Kansas City list in 1913 and disliked it. Older lists had given October beryl. In the eight he compared, beryl, often as aquamarine, appeared for October in every one, and opal in only one. He also objected to tourmaline, which had been known as a gem only since the eighteenth century.

The list has been revised since. In 1952 the Jewelry Industry Council proposed pink tourmaline as the alternate to opal, and the American Gem Society and the National Retail Jewelers Council approved it. Trade accounts often say tourmaline was added in 1952, but Kunz's 1913 printing already shows it as October's alternate. Later revisions added tanzanite for December in 2002 and spinel for August in 2016, and left October alone. GIA lists opal as the traditional October stone and tourmaline as the newer one.

What play of colour is

Precious opal is made of tiny spheres of silica stacked in a regular grid. Light passing between the spheres is diffracted and split into spectral colours, and the size of the spheres decides which colours appear: the smallest give violet, larger ones red. The shifting patches of colour this produces are called play of colour. Opal without it is common opal.

How to choose an opal

  • Brightness. GIA ranks the brightness of the play of colour first, then the range of colours. Red has traditionally been valued most, then orange, then green.
  • Pattern and direction. Large, closely set patches are preferred to scattered pinpoints. The best stones show colour from every angle; patches with no colour lower the value.
  • Body tone. A dark background makes the colour stand out, which is why black opal is prized. White and crystal opal are more common.
  • Cut. A well-rounded dome shows colour best. A flat, thin cabochon breaks more easily, and thin opal is often glued to a backing as a doublet or capped with quartz or glass as a triplet, so ask whether a stone is solid.
  • Care. Opal is 5 to 6.5 on the Mohs scale and can be scratched by harder gems. Clean it with warm soapy water and keep it away from heat and sudden changes of temperature.

Opal from Ethiopia

GIA names Australia as the most productive source of opal and Ethiopia among the other important ones. A deposit near Wegel Tena, in Wollo, was found in 2008, and in 2015 a research director at Gemworld International told JCK that Ethiopia had been the most important source by volume for at least five years. The Wollo opal is mostly white, with some crystal, fire and brown opal, and its play of colour is often vivid. Much of it is hydrophane: it absorbs water and can look clearer when wet, so compare stones dry.

October's other stone now has an Ethiopian source as well. In August 2026, GIA and the Gübelin Gem Lab confirmed Ethiopia as a new source of copper-bearing tourmaline of the kind sold as paraíba.

Buying opal from us

We offer opal rough in wholesale parcels, and single stones on request. Each selection shows unedited photographs and video, with weights and pricing. If you are looking for tourmaline, ask us.

Sources

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