Baltic amber and pyrite: two of nature's timeless wonders

Here at Stump Cross Caverns, we're mad about geology. That's why this winter, we're holding workshops dedicated to two remarkable materials: pyrite, commonly known as fool's gold, and Baltic amber.

We first got excited about pyrite when Nick and Lisa (AKA Cavewoman) visited Victoria Mine in Navahun, Spain, and marvelled at the cubic pyrite crystals there. These beautiful specimens were millions of years old. Wow! 

We simply had to bring them to Stump Cross so visitors could get a look.

Then there's Baltic amber, a beautiful, ancient material formed from fossilised tree resin. Each piece of amber has travelled many miles over millions of years.

But that's just the beginning. Let's find out more about these two timeless wonders…

What is pyrite?

Pyrite, or iron sulfide, is commonly known as "fool's gold". It's often found in the same place as gold and sometimes shines like gold. This has led many a miner to be fooled into taking home something less valuable – but no less fascinating.

The word "pyrite" comes from the Greek word for fire, pyr (think "pyromaniac"). This is because it can create sparks when struck against metal or stone. Ancient civilisations used it for fire-lighting and modern societies used it for firearms. In the south of Thailand, it's said to ward off evil, black magic and demons.

Today, it's mainly used for jewellery. It's also highly useful in the search for gold, as the two often form together. But how is it formed?

Well, the ancients believed it was formed deep within the Earth and brought to the surface by volcanic activity. Today, scientists tell a different story. Bacteria reduce sulfate ions in underground water, creating sulfide. This then reacts with iron to form pyrite.

It's found in many places: igneous, sedimentary and metamorphic rocks, hydrothermal mineral deposits and coal beds.

And like amber, it's exceptionally good at preserving fossils. In 2024, for example, researchers cracked open a piece of pyrite to discover a 450-million-year-old spider!

The specimen was so well preserved that Luke Parry, who led the research team, remarked, "They look as if they could just get up and scuttle away".

What is Baltic amber?

Every piece of amber, Baltic or otherwise, has a long and storied history.

It begins with a tree getting cut or knocked. To protect itself against disease, the tree oozes resin, forming a natural scab over its wound.

The resin flows down to the forest floor and becomes embedded in the sediment. On the way down, it can trap insect or plant life.

Millions of years pass. A chemical substance called terpenes breaks down and leaves the resin. The result is amber.

This process happened millions of years ago in the forests of Northern Europe. So, how did pieces of Baltic amber end up on the shores of the UK?

Over the last two million years, glaciers melted and shifted amber deposits towards the Baltic shorelines. Storms churned the sea bed and sent them out to sea, ending up on foreign shores.

Amber has remarkable fossilising properties. Most amber inclusions are insects and arachnids, some trapped in motion. But amber can also fossilise lizards, dinosaur feathers, plant species and even birds.

Most specimens of amber are, well, amber. But they come in a surprising array of colours – from white to citrus yellow, from brown to black.

Today, amber is used for jewellery and lends its distinctive pinewood scent to some perfumes. Some people believe it has restorative properties.

What is the oldest material on Earth?

Pyrite and amber are astonishingly old. But did you know that the oldest material on Earth is 7.5 billion years old?

Scientists found dust grains within a portion of the Murchison meteorite that fell to Earth in 1969. These grains are older than our Solar System, which is a spring chicken at 4.6 billion years old.