The Geology of Rock Park

How old are the rocks in Rock Park?

The rocks in the park were formed in the Silurian Period, approximately 430 million years ago. The rocks are the Builth Mudstones Formation, made of mud and silt that were deposited in a sea that once covered Wales.

Why are there mineral springs in Rock Park?

A mass of granite lies under the Builth–Llandrindod area. Water percolating through the granite picks up elements such as lithium and iron from the rock. Rainwater sinking down from the hills mixes underground with water moving upwards from the granite. The mixed water moves upwards through fractures and faults in the rock and comes out at the surface as mineral-rich springs.

In Victorian times, several springs could be drunk from in Rock Park, including a chalybeate (iron) spring, a lithium well, a sulphur well, and a magnesium well. Only the chalybeate spring is still accessible.

What is in the mineral water?

The chalybeate spring water contains high levels of chlorine, sodium, and calcium, and notable levels of other elements, including iron. The spring water does not include worrying quantities of uranium or radon, but does contain more lead than the permitted level in drinking water.

Data sources:

• chemistry of Rock Park chalybeate spring water from Edmunds et al. (1998); chemistry of Radnor Hills mineral water from Smedley (2010).
• Edmunds, W.M., Robins, N.S. & Shand, P., 1998. The saline waters of Llandrindod and Builth, Central Wales. Journal of the Geological Society, London, 155, 627–637.
• Smedley, P.L., 2010. A survey of the inorganic chemistry of bottled mineral waters from the British Isles. Applied Geochemistry, 25, 1872–1888.