Shap Granite - Parliament Square EarthCache

Welcome to Parliament Square

Standing before the statue of Henry John Temple, 3rd Viscount Palmerston, you’ll find more than just a monument to a Victorian statesman. The granite pedestal beneath him is itself a piece of Earth’s deep history. This stone, known as Shap Granite, was formed from slowly cooled magma deep within the crust of what is now northern England over 390 million years ago. Through this EarthCache, you’ll explore how mineral composition, crystal growth, and human craftsmanship combine to make this granite both a geological wonder and a symbol of endurance in the heart of London.

The Story of Shap Granite

Shap Granite is one of Britain’s most distinctive granites, quarried near the village of Shap in Cumbria, northwestern England. It formed during the Devonian Period, roughly 394 million years ago, when molten rock intruded into older sedimentary layers deep underground. The slow cooling of the magma over tens of thousands of years produced large, interlocking crystals visible to the naked eye today.

This granite is known for its porphyritic texture, with large pink orthoclase feldspar crystals, or megacrysts, set within a finer-grained background of quartz, plagioclase, and biotite mica. The sparkling contrast between pink feldspar, grey quartz, and dark biotite gives the rock a striking appearance. Its hardness and interlocking crystalline structure make it exceptionally strong and resistant to weathering, which is why it has been widely used for architecture, monuments, and engineering projects, including the pedestal of the Palmerston statue. Shap Granite exists in several varieties, most notably Dark Shap, with a deeper pink hue and fewer flaws, and Light Shap, which is slightly paler and more open-textured. Both share the same mineral composition, but visual differences and crystal distribution influence their use.

Shap Granite also provides a clear lesson in Earth processes. The large feldspar megacrysts indicate very slow cooling deep underground, while the finer-grained surrounding minerals crystallized more quickly, showing a two-stage cooling process typical of intrusive igneous rocks. Over centuries, the granite was quarried using traditional techniques, transported across Britain, and chosen by Victorian architects and sculptors for its durability, visual appeal, and symbolic permanence in public monuments.

Tasks for This EarthCache

To log this EarthCache, visit the site and complete the following tasks. Send me your answers via Geocaching or email.

1. Include "Shap Granite - Parliament Square - GCBEAC3" on the first line of your message.

2. Observe the granite closely. What colors can you identify in the pedestal? Describe the differences between the large pink crystals and the surrounding minerals.

3. Estimate the size of the largest feldspar crystals you can find. Are most of the megacrysts small, medium, or large? What does this suggest about the rate of cooling when the rock formed?

4. Look for signs of weathering. Do you notice any cracks, chips, or discoloration on the granite? Based on what you see, do you think Shap Granite was a good choice for this pedestal?

5. In your log, attach a photo of yourself or a personal item with the statue of Henry John Temple in the background. (Note: photos predating the publication of this EarthCache are not accepted.)

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