What is the BIF slab?

Article | Updated 9 months ago

It weighs 8.8 tonne (roughly a third the weight of a bus), it’s 2.5 metres high and 3 metres wide (one and half time higher and three and half times wider than an average doorway), and it’s about 3,000 million years old.

And it tells the story of Western Australia.

The size of the slab is truly impressive.
Image copyright WA Museum 

This particular piece of Banded Iron Formation is from the Ord Ranges in the northern Pilbara. It is a new acquisition for the State Collection and is being considered for the New Museum. What is a Banded Iron Formation? Well that’s part of why this object tells the story of Western Australia.

Banded Iron Formation or BIF (pictured above) gets its name from the bands of finely layered iron-rich sediment from which it is formed. The different bands of colour in the BIF slab are r iron oxides and red and brown chert, and golden-brown tiger eye (a type of fibrous quartz).

Western Australia has some of the biggest deposits of banded iron formations in the world and much of the State's prosperity can be contributed to iron ore in rocks like this. Western Australian iron ore is traded to global partners and has created strong economic relationships with the USA, China and elsewhere.

Just like Western Australia, this piece of BIF is big and it’s incredibly old – as old as the Pilbara landscape it came from.

Karijini National Park in the Pilbara is one of the world’s most famous spots to see this type of rock formation. It's also a place of deep cultural value to the Banyjima, Kurrama and Innawonga Aboriginal people who have occupied the land for at least 20,000 years.

BIF is also part of the story of the formation of landscape and environments we know today.

Most of the BIF of the Pilbara region were deposited on the ancient seafloor about 2700 to 2400 million years ago and may have resulted, in part, from the action of the earliest life forms on Earth. At this time, masses of cyanobacteria in the ocean photosynthesised, producing oxygen like many modern plants.

The accumulation of oxygen in seawater caused the iron present to oxidize. The ocean ‘rusted’ and iron-rich minerals were deposited to form BIFs. Early life continued to produce oxygen that enriched the atmosphere and set scene for the environment we know today, the basis for life on Earth.

This piece of BIF is truly magnificent. It’s been cut and polished – no mean feat for an 8.8 tonne piece of rock.

What you see looks more like a deliberate work of art than the product of a restless Earth. The bands in most pieces of BIF are flat lying, but this piece has folded and kinked bands.

It’s been tortured under the stress of slow movements within the Earth along the northern edge of the Pilbara millions of years ago.

It holds the story of our Earth and our place, and the story of a time long, long before us.

Close up of the BIF Slab shows the different bands of iron in the rock formation

Up close you can see the folded kinked bands of the BIF slab.
Image copyright WA Museum