My interest in ochre was rekindled recently, when I explored the Claypit Nature Reserve near Wickepin. Years ago as part of a mining lease there, the side of a mesa was excavated to get adjoining white and red ochre clays for brickmaking. The white section formed over granite, and red over a dolerite dyke.
 Side view. dolerite dyke under red ochre band |  Front view facing south |
The importance of ochre for first nations people is summarised in this article on the ancient Weld Ranges Ochre mine.
An ochre pit at Dryandra National Park is one of over 440 recorded around Australia. For a nation this large, it is a small number, hence the value of ochre as an item of trade.
An ochre pit at Dryandra National Park is one of over 440 recorded around Australia. For a nation this large, it is a small number, hence the value of ochre as an item of trade.
What is ochre and where is it found?
Charcoal and in some areas coal was the basis of black ochre, which was crushed and mixed with a fluids such as water, saliva, blood or fat as a sticking agent.
Other ochres are mineral oxides attached to a white non-cracking clay called kaolinite, particularly in subsoils in the wheatbelt and rangeland uplands. In Australia this clay has formed as a deep layer underneath mesas, which are ancient remnants of ancient lateritic land surfaces.
Charcoal and in some areas coal was the basis of black ochre, which was crushed and mixed with a fluids such as water, saliva, blood or fat as a sticking agent.
Other ochres are mineral oxides attached to a white non-cracking clay called kaolinite, particularly in subsoils in the wheatbelt and rangeland uplands. In Australia this clay has formed as a deep layer underneath mesas, which are ancient remnants of ancient lateritic land surfaces.
A good local example is the Uellelling Hill kaolinite mine east of Wickepin. The image below of a cutting in the exploration phase displays typical layers of an old laterite profile.
- The gravel layer contains most of the plant roots.
- The mottled zone layer is a transition to the pallid zone layer, which is stained by iron leaking down from the gravel layer.
- The pallid zone layer is decomposed bedrock, which has been weathered to clay and sand, and infilled with extra clay
Uelling Hill exploration pit
The clay is a type of kaolinite called halloysite, which has many uses ranging from fine porcelain, paint additive, medicine and dentistry. Unlike other clays halloysite consists of microtubes rather than sheets.
Electron microscope images of halloysite forming around bacteria lead on to a great story of soil development where plants lift minerals up from the depth in soil water, and microbes and fungi convert them to lateritic gravels, bauxite or clays.
Electron microscope images of halloysite forming around bacteria lead on to a great story of soil development where plants lift minerals up from the depth in soil water, and microbes and fungi convert them to lateritic gravels, bauxite or clays.
Pallid zone clay is also packed with salt, which was uplifted with soil water by native trees. When land was cleared, this salt washed down into rising groundwater and created our severe wheatbelt salinity problem.
Lake Taarblin was a freshwater lake before widespread agricultural land clearing
White dams dotted around our landscape show the widely distributed pallid clay. If early Noongars had bulldozers, ochre would have been easy to get!
However, ochre only outcrops naturally on breakaway slopes. Granitic breakaways contain white ochre and less commonly yellow ochre (which contains an iron oxide called limonite). Red ochre contains an iron oxide called haematite which is mostly found on steep red-brown breakaways, which have formed off very iron-rich rocks such as dolerite. Green ochre (containing a nickel oxide) is rare, only being found on ultramafic rock breakaway areas such as the Goldfields.
Good ochre contains very little sand.
However, ochre only outcrops naturally on breakaway slopes. Granitic breakaways contain white ochre and less commonly yellow ochre (which contains an iron oxide called limonite). Red ochre contains an iron oxide called haematite which is mostly found on steep red-brown breakaways, which have formed off very iron-rich rocks such as dolerite. Green ochre (containing a nickel oxide) is rare, only being found on ultramafic rock breakaway areas such as the Goldfields.
Good ochre contains very little sand.
 Granitic breakaway at Hyden |  Cave in Tutanning Nature Reserve dolerite breakaway |
To see a jaw dropping breakaway, visit Buckley's Breakaway 70km east of Kulin
Buckley's Breakaway
I found an easy way to make good ochre.
- Put the ochre sample in a bucket and add enough water to make liquid
- Swirl the liquid vigourously, then pour clay and water slurry off into another bucket leaving sand behind
- Leave the water and clay for a couple of days until the clay settles out leaving water above. Adding salt may help.
- Pour off the water leaving the clay slurry behind to evaporate to a creamy consistency