Opal Belemnite - Ancient Sea Creatures Turn Into Gemstones


[Read Time: 5 Minutes]

Every serious opal enthusiast wants to have an opalized belemnite fossil in their opal collection. Belemnites are ancient Cephalopods from around 100 million years ago. Most opalized belemnites are found only in the South Australian opal fields around Cooper Pedy. Ancient cephalopods were squid like creatures that are related to the Octopus and Cuttlefish.


  • Belemnite are ancient sea creatures
  • Once deceased they leave a cavity in the clay which is filled with Opal
  • The most famous Belemnite is the Virgin Rainbow

What Are Belemnites

Belemnites are found in many countries including Sweden, England, Morocco and the USA. These creatures were prolific swimmers and vast quantities existed on earth but only Australian belemnites from Cooper Pedy are opalized. Beleminte fossils can be found in host rock all around the world. However in Australia the cavities left behind byu the Belemnite was filled with Opal instead of other material such as Quartz. This is why Australia is the only place in the world where Opalized Belemnites are found.

what are belemnites

This make them a must have for opal enthusiasts. But they are very rare and to find one with full opal colour is very expensive. A torpedo shaped belemnite with translucent opals colours spectrum are extremely expensive. Most of the time they are found broken into pieces. Broken belemnites with clear or light sea blue colours are still reasonable priced.

Other ancient Cephalopoda include other molluscs such as

  • Octopuses
  • cuttlefish
  • nautilus

If you find a parcel of rough opal make sure you look for these. Octopus is extremely rare but there have been some findings in the past.

opalzied shells from coober pedy

Belemnites were different to modern day squids as they had internal skeleton and no tentacles like modern squid. They had ten arms with studded hooks instead tentacles. In scientific community they are called Belemnitida (genus) belemnites, extinct cephalopods from Mesozoic to upper cretaceous era. Belemnoids were squids but more closely resembled the cuttlefish.

The World’s Most Famous Belemnite is The Virgin Rainbow

A 72 carat Black Crystal Opal belemnite fossil found in 2003. This opal is on display at Adelaide Museum celebrating 100 years of opal mining in the state. The exhibition is called simply OPALS.

virgin rainbow opal

Also on display is a six-meter Plesiosaurus that has an opalescent sheen in its skeleton.

South Australia was once under sea water in prehistoric times which was filled with marine creatures like aquatic reptiles. The director of the museum is excited to show opals that were formed when South Australia was under the sea and dinosaurs walked the planet. Compared to the famous opal mines at Lighting Ridge in New South Wales which were fresh water rivers and swamps so different prehistoric species are found in this area like mussel’s shells, pine cones etc.

opalized belemnites from Seda opals

The specimen pictured above is in the Seda Opals collection and consists of two belemnites a rare black crystal opal and a rare multi fire crystal opal.

How Does A Belemnite Become Opalized?

When a belemnite died it would sink to the bottom of the sea and the sediment on the floor would be very muddy from the clay based soils. The decaying body would have been covered in this clay sediment very rapidly and stayed there for millions of years in desert type conditions.

After the sea eventually dried up the acidity in the sandstone soil greatly increased and the silica gel from the sandstone escaped and filled in crevices in the clay and in some areas these belemnites were encased in clay.

Over millions of years the acidic levels dropped and the silica gel hardened into opal in impressions of the decayed squid. This process was not common and most belemnites do not have opal colours. It is extremely rare to find multi colour opal or black crystal opal like the virgin rainbow.

It is understanding the rarity of this opal that makes one appreciate how rare and unique it is for mother nature to have produced such a spectacular belemnite opal

What Are Opal Pipes

Opal pipes should not be confused with Belemnites. They are cylindrical shaped not torpedo shape and are found in many opal fields. They are formed in ironstone/sandstone potch.

opal pipe

These crystal pipes can be small only 1-2 mm wide or up to 12mm diameter and can be hollow or filled. These tubes are known as breccia pipes. Theory is that the hollow tubes had water running through them when formed and there is no relationship with prehistoric animals. Many opal pipes are cut into boulder crystal stones and sold with realizing that they were pipe opal.

Shop For Belemnites

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Opal fossils, including belemnites, have been recovered from Coober Peedy and another location, Mintabie, situated about 300 km from Coober Peedy. As of July 1, I 2019, the area will revert from government to aboriginal control, under the APY. Leases have not been renewed and the mines are expected to close.

8th Jun 2019

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