This cache has been placed with the permission of Parks Australia who have also supplied some of the information provided in this Earth Cache. We acknowledge the traditional owners and ask that you respect this very sensitive area; taking only photographs and leaving only footprints.
The thousands of people who visit the art sites each year pose the greatest, although unintentional, threat to the rock art. To help protect the paintings please: Do not touch the paintings or interfere with the silicon drip lines Keep to the walking tracks and behind the fences and barriers Do not enter prohibited areas Penalties apply to anyone defacing.
The colours in the Kakadu rock art paintings come from several naturally occurring ‘rocks’ (using that term loosely).
To make the paint used in the rock art, pigments commonly referred to as Ochre were crushed on a stone palette and mixed it with moist ingredients such as water, saliva, plant resins and in some cases even blood to make a paste. Brushes were made from human hair, chewed sticks, reeds and feathers. Sometimes, wet pigments were blown from their mouths around objects, to create a stencil. You can see hand stencils like this at Ubirr and Naguluwurr.
So where does the array of colours come from?
The short answer most people will give you is Ochre. By definition Ochre is a clay that is coloured by varying amounts of hematite, varying between 20% and 70%. Red ochre contains unhydrated hematite, whereas yellow ochre contains hydrated hematite (Fe2O3 • H2O). The principal use of ochre is for tinting with a permanent colour.
Like Ochre, Kaolin (Used to make white in rock art.) is a clay and can be commonly seen right across Australia. In its pure white form it doesn’t receive any pigment/colour form iron oxides. Kaolin has the chemical composition Al2Si2O5(OH)4. It is a layered silicate mineral, with one tetrahedral sheet of silica (SiO4) linked through oxygenatoms to one octahedral sheet of alumina (AlO6) octahedral.
To properly explain the array of colours we must also talk about Iron oxides; they are the chemical compounds responsible for the variety of colours composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides. Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely used by humans, e.g., as iron ores, pigments, catalysts, in thermite and hemoglobin. Common rust is a form of iron(III) oxide. Iron oxides are widely used as inexpensive, durable pigments in paints, coatings and colored concretes. Colors commonly available are in the "earthy" end of the yellow/orange/red/brown/black range and can be traced back as far as 75,000 years ago.
Haematite - An iron-rich rock most commonly used to make red in rock art. is the mineral form of iron(III) oxide (Fe2O3), one of several iron oxides. Hematite can be colored black to steel or silver-grey, all the way through the to bright red. It is mined as the main ore of iron. Varieties include kidney ore, martite, iron rose and specularite. While the forms of hematite vary, they all have a rust-red streak. Hematite is harder than pure iron, but much more brittle. Huge deposits of hematite are found in banded iron formations like those in Central, North and Western Australia which makes it one of the most common pigments used.
Limonite and goethite - Used to make yellow/orange in rock art.
Limonite is an iron ore consisting of a mixture of hydrated iron(III) oxide-hydroxides in varying composition. The generic formula is frequently written as FeO(OH)·nH2O, although this is not entirely accurate as the ratio of oxide to hydroxide can vary quite widely. Limonite is one of the two principal iron ores, the other being hematite, and has been mined for the production of iron since at least 2500 BCE. Limonite usually forms from the hydration of hematite and magnetite, from the oxidation and hydration of iron rich sulfide minerals, and chemical weathering of other iron rich minerals such as olivine, pyroxene, amphibole, and biotite. It is often the major iron component in lateritic soils.
Goethite is an iron oxyhydroxide containing ferric iron. It is the main component of rust and bog iron ore. Goethite often forms through the weathering of other iron-rich minerals, and thus is a common component of soils, concentrated in laterite soils. The formation of goethite is marked by the oxidation state change of Fe2+ (ferrous) to Fe3+ (ferric), which allows for goethite to exist at surface conditions. Because of this oxidation state change, goethite is commonly seen as a pseudomorph. Goethite is usually found in the form of concretions, stalactitic formations, oolites , reniform or botryoidal accumulations. It is commonly found in the swampy areas at the head of spring waters ('bog iron'), on cave floors, and on the bottom of lakes and small creeks.
Manganese oxide and charcoal - Used to make black, although charcoal is not a mineral and does not last long. Manganite is a mineral composed of manganese oxide-hydroxide, MnO(OH). Manganite occurs with other manganese oxides in deposits formed by circulating meteoric water in the weathering environment in clay deposits and laterites. It forms by low temperature hydrothermal action in veins in association with calcite, barite, and siderite. Often associated with pyrolusite, braunite, hausmannite and goethite.
Of all the paints, haematite lasts longest. This is why the majority of old paintings that you see today are completely red.
To log this Earth Cache we require you to visit each of the Rock art sites along the 1.5km walk, consider the information given and available to you at the site then message us with the following answers to the best of your ability;
1. Along the walk you will see two at least two Kangaroos in two different colours, which minerals were used on each of these Kangaroo’s?
2. Find Nabulwinjbulwinj, identify the minerals most likely used in his body?
3. Visit Lightning Man, in relation to colour how does he compare to Nabulwinjbulwinj, why do you think this is the case?
4. What is the main rock type forming the canvas for the art here?
5. Can you see signs of weathering/fading? Describe what you see.
6. A photo of your team or GPS near some art work ( not giving any answers away), we can't get enough of this place so upload as many photos as you like! (Optional)
You are welcome to log your answers straight away to keep your TB's and Stats in order but please message us with your answers within 1 week. Cachers who do not fulfil the Earth Cache requirement will have their logs deleted without notice.
Source Parks Australia, Wikipedia
