The Only Place on Earth You Can Find This Rock

The Unique Rock Found In Only One Place on Earth

On the quiet western edge of the Kennedy Ranges, the ground looks plain and unremarkable. Cretaceous sedimentary rocks lie exposed in shallow ridges, and the dry creek beds hold scattered fragments of chert, iron-stained jasper, and silica nodules that blend easily into the muted colours of the desert. There is nothing about this landscape that suggests a globally recognisable gemstone lies beneath it. To most people passing through, these stones would seem like nothing more than weathered debris from an ancient rock unit, the kind of material that accumulates in every dry gully across Western Australia. Yet this ordinary-looking terrain hides a geological secret that almost nobody outside a small circle of collectors and geologists knows exists.

*Image depicts the location of Mooka Creek.

The truth is that these quiet outcrops and creek beds mark the surface expression of a unique rock found nowhere else on Earth that began its life not in a desert, but in a deep marine environment, built from microscopic organisms whose glassy skeletons once blanketed the seafloor. Over millions of years, those siliceous remains hardened, cemented, and transformed, and later received pulses of iron-rich fluids that produced the vivid colours that make the stone instantly recognisable once polished. The connection between the present landscape and its ancient origin is invisible to the casual observer. Only by reading the rock carefully does the story emerge.

*Image is of a Mookaite specimen.

It is difficult to imagine that this arid plain was once covered by a broad, open ocean—an ocean so different from today that almost nothing in the modern landscape hints at its former presence. The contrast between the vanished seafloor and the dry desert is so extreme that the link between them would remain unknown if not for the rock itself. And yet, despite the uniqueness of the gemstone produced here, very few people are aware of its geological significance. Lapidarists and fossickers know the polished material. Some collectors know its trade name. But beyond that, the true origin of the stone and the reason it occurs only in one small region remain obscure, even among many who work with rocks and minerals regularly.

*Image depicts the extent of the Cretaceous ocean.

Part of the reason is that the geological conditions that shaped this material were extraordinarily specific. A series of processes had to align in a precise order: biological sedimentation in a silica-rich sea, burial and diagenesis into porcellanite, secondary silicification, iron mobilisation, uplift, and selective erosion. This combination occurred only once, in one basin, during one interval of geological time. That singular chain of events produced a rock with colours and patterns the natural world does not recreate elsewhere. And that is why this stone—known to gem lovers simply as Mookaite—remains tied exclusively to Mooka Creek in Western Australia.

To understand how it formed, it helps to return to the beginning, when this part of Australia lay beneath the waters of the mid-Cretaceous Carnarvon Basin. In that ancient ocean, radiolarians flourished in immense numbers. These tiny plankton build delicate skeletons out of silica, and when they die, their remains drift downward like microscopic snow. Over time, their glassy skeletons accumulated in thick layers on the seafloor, forming a siliceous mud known as radiolarian ooze. In regions where radiolarians were particularly abundant, these siliceous sediments can be hundreds of metres thick. In Western Australia, they became the Windalia Radiolarite—a key rock unit that preserves the earliest stage of Mookaite’s formation.

Once deposited, the radiolarian ooze began a long transformation under the weight of overlying sediments. Burial compresses siliceous mud, squeezing water out and dissolving some of the silica, which then reprecipitates in denser forms. Over millions of years, this process turns soft sediment into increasingly hard material. The Windalia Radiolarite passed from opaline silica into a dense, porcelanous rock called porcellanite. Porcellanite is extremely fine-grained and tough, with a texture that resembles unglazed porcelain. This geological hardening erased most traces of the original radiolarians but preserved the silica that would eventually form the base of Mookaite.

Geological documentation describing decorative stones of Western Australia notes that Mookaite consists of “massive ultrafine silica,” a direct result of this diagenetic process preserved within the Windalia Radiolarite. The porcellanite stage is important because it sets up the rock for the next transformation. It forms a stable, low-porosity framework strong enough to withstand later chemical alteration without collapsing or becoming friable. Without this early hardening, the stone would not have become durable enough to endure the next stages of its evolution or survive millions of years of erosion after exposure.

A second transformation occurred when silica-rich groundwater infiltrated the rock. This groundwater was drawn from surrounding bedrock and carried dissolved silica in solution. As it moved through the radiolarite, it deposited this silica along fractures, pores, and grain boundaries. This was not a superficial coating—it permeated deeply, adding a new generation of microcrystalline silica that solidified the porcellanite even further. The result was a dense, cryptocrystalline material capable of taking a polish far superior to most sedimentary rocks. This secondary silicification also sealed the rock, giving it the ability to preserve sharp, vivid colour boundaries during the iron-staining event that followed.

The iconic colours of Mookaite appeared when iron-bearing fluids passed through the rock long after the initial silicification. These fluids were part of the region’s groundwater system, enriched with iron from other rocks in the basin. As the fluids moved through cracks and tiny diffusion pathways, the iron oxidised and precipitated as various minerals. Hematite created strong reds and burgundies. Goethite and limonite produced yellows, tans, and browns. In rare instances, subtle shifts in chemistry allowed for purples influenced by manganese or organic compounds. Areas untouched by iron remained pale cream or white.

*Image depicts the Windalia Radiolarite (dark brown) with silica rich ground water infiltrating the layer (white) along with iron bearing fluids (orange). 

The distribution of these colours is irregular because the movement of iron-rich fluids was influenced by micro-scale variations in the rock’s structure. Sometimes the iron invaded a zone abruptly, leaving a sharply defined boundary. Other times it diffused slowly, creating soft gradients. In places where the rock fractured during burial and later healed with silica cement, contrasting colours filled the cracks, producing brecciated or mosaic-like patterns. The result is a natural artwork produced not by surface staining but by mineral pigments locked inside a silica matrix. Every piece is a record of fluid movement and chemical changes that cannot be replicated artificially.

After the rock’s formation underground, it remained hidden until tectonic forces slowly lifted parts of the Carnarvon Basin. Erosion carved away the softer overlying sediments, gradually exposing the Windalia Radiolarite. As the desert landscape formed, seasonal runoff cut gullies and creeks into the radiolarite. The hardest, most silicified portions resisted weathering and broke into durable nodules and blocks that washed into stream channels. Mooka Creek, the locality that gave the gemstone its name, became a natural repository of these fragments. Unlike gemstones mined from massive outcrops, Mookaite commonly appears as float material liberated from its host rock by long-term erosion.

*Image depicts the erosion of softer rocks above the Windalia radiolarite, along with gullies carved into it which liberate Mookaite and deposit it into stream float.

Although often referred to as jasper in the gem trade, Mookaite is not a true jasper in the geological sense. Jasper typically forms from volcanic ash deposits or strongly silicified mudstone, whereas Mookaite originates from radiolarian microfossils transformed by burial and chemical alteration. It differs from ordinary chert, which usually lacks the vivid colour patterns created by iron mobilisation. It also differs from pink opal found in the same region, which represents a hydrated form of silica within similar radiolarian rock. Because of these distinctions, geological references classify Mookaite as a silicified radiolarite rather than as a jasper, even though it behaves like jasper when polished.

Its unusual durability, high silica content, and ability to take a strong polish make Mookaite valuable for lapidary work. Its colours remain stable because they are mineralogical rather than organic, and its internal structure lacks the planes of weakness that sometimes affect volcanic jaspers. This has made Mookaite sought-after worldwide for cabochons, beads, carvings, and decorative pieces. Its patterns are varied enough that no two pieces look alike, which adds to its appeal among collectors.

Scientifically, the stone serves as a geological archive. The radiolarian origin records ocean conditions during the mid-Cretaceous, offering insight into marine silica cycles. The porcellanite stage preserves evidence of diagenesis in a marine basin. The secondary silicification reflects changing groundwater chemistry and the movement of silica through the crust. The iron staining records oxidation conditions and fluid pathways. And the present-day exposures illustrate the tectonic and erosional history of the Carnarvon Basin. Each polished specimen carries traces of this entire sequence.

What makes the stone truly remarkable is the improbability of its formation. A nutrient-rich sea had to support vast populations of radiolarians. Their remains had to accumulate in significant quantities. Burial had to transform this mud into porcellanite. Silica-rich groundwater then had to enter the rock at the right time. Iron-bearing fluids had to follow. Uplift had to bring the material to the surface. And erosion had to expose it without destroying it. This chain of events occurred only once, which is why the stone remains exclusive to Mooka Creek and why so few people outside specialised circles understand its origin or significance.

Mookaite stands today as one of Western Australia’s most distinctive geological materials. Its colours resemble the desert around it, but its origin is tied to a vanished ocean. Its patterns reflect interactions between microscopic life, groundwater, and deep time that no other stone captures in the same way. It remains a geological outlier—a material shaped by conditions so specific that it will likely never form again.

Here's the video we made on this on the OzGeology YouTube Channel:

Studies Used To Construct This Article:

Gemstones of Western Australia 

Mookaite A Western Australian Ornamental Rock