A thunderegg (or thunder egg) is a nodule-like rock, similar to a filled geode, that is formed within rhyolitic volcanic ash layers. Thundereggs are rough spheres, most about the size of a baseball—though they can range from less than an inch to over a meter across.
A thunderegg (or thunder egg) is a nodule-like rock, similar to a filled geode, that is formed within rhyolitic volcanic ash layers. Thundereggs are rough spheres, most about the size of a baseball—though they can range from less than an inch to over a meter across. They usually contain centres of chalcedony which may have been fractured followed by deposition of agate, jasper or opal, either uniquely or in combination. Also frequently encountered are quartz and gypsum crystals, as well as various other mineral growths and inclusions. Thundereggs usually look like ordinary rocks on the outside, but slicing them in half and polishing them may reveal intricate patterns and colours. A characteristic feature of thundereggs is that (like other agates) the individual beds they come from can vary in appearance, though they can maintain a certain specific identity within them.
Digging for thunder-eggs great fun”
We went to Thunderbird Park to visit the Thunder-egg Mine and fossick for Thunder-eggs. Its located on Mount Tamborine and is easy to get too. The drive is very scenic. The park has caravan and tent accommodation sites and also has upmarket chalets. Also at the park is a nice restaurant and cafe that makes good food. Other facilities there is a adventure area and also horse riding (separate fees). Entry fees to the mine area included an informative explanation on thundereggs, how to find them, a mine safety talk, as well as the use of a pick and bucket to collect the rock. You get to take home all the thundereggs that fit inside the rim of your bucket. When you bring the thunder-eggs back to the counter they will sort them and tell you which are good and bad. They then offer a service to cut the best ones open in half for a small fee. It does take some effort to climb a steep hill to get to the place were the thunder-eggs are and if your not to fit it can be hard on the body. The mine is above ground on the edge of the hill. Our kids (6 and 8 years old) enjoyed it very much but the effort to dig in the clay can be hard for them but it kept them amused for a couple of hours. Expect to get a little dirty digging with a pick. They have pre cut eggs in the shop. Only negative is entry fee to the mine is a little pricey especially if you end up the only one digging but otherwise a good day out in Mount Tamborine.