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Mooralla, Southern Grampians Shire, Victoria, Australia

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Latitude & Longitude (WGS84): 37° 20' 49'' South , 142° 3' 4'' East
Latitude & Longitude (decimal): -37.34694,142.05111


Since the 1960s smoky quartz 'geodes' have been highly sought after from the designated gem collecting site near Mooralla, near the Grampians in western Victoria. The geodes are formed below the surface in weathered greenish-grey rhyolite, known as the Rocklands Rhyolite, which erupted in the Late Devonian period. Decades of collecting have resulted in a landscape of low dumps, partly filled in pits and holes as deep as six metres in an area where good specimens were once recovered from close to the surface.

The predominantly smoky quartz crystals, very dark brown to black in colour, are noted for their transparency and lustre, and often contain wispy swirls and gas bubbles in fluid inclusions. They are found as simple to complex crystals or groups of crystals up to three or four centimetres across and loose crystals, weathered out of the rhyolite, are common. Most valued are spherical geodes up to 10 centimetres across, with one or more crystals attached to the inside walls of the geode.

The inside walls of the geodes are often lined with small opaque and colourless quartz crystals up to a few millimetres long, and sometimes amethystine to pink or lilac quartz of similar size.

Mineral List

Mineral list contains entries from the region specified including sub-localities

5 valid minerals.

Regional Geology

This geological map and associated information on rock units at or nearby to the coordinates given for this locality is based on relatively small scale geological maps provided by various national Geological Surveys. This does not necessarily represent the complete geology at this locality but it gives a background for the region in which it is found.

Click on geological units on the map for more information. Click here to view full-screen map on Macrostrat.org

Early Devonian
393.3 - 419.2 Ma
Rocklands Volcanic Group

Age: Early Devonian (393.3 - 419.2 Ma)

Stratigraphic Name: Rocklands Volcanic Group

Description: Subaerial caldera volcanics: rhyolitic ignimbrite, minor rhyolitic lava, fluvial sandstone

Comments: igneous felsic volcanic; synthesis of multiple published descriptions

Lithology: Igneous felsic volcanic

Reference: Raymond, O.L., Liu, S., Gallagher, R., Zhang, W., Highet, L.M. Surface Geology of Australia 1:1 million scale dataset 2012 edition. Commonwealth of Australia (Geoscience Australia). [5]

Data and map coding provided by Macrostrat.org, used under Creative Commons Attribution 4.0 License


Localities in this Region

Australia

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