Darwin wrote "Porphyry; summit of peak. (Crystals larger, fatter, hardly any cleavage, feldspar??)"
Thin reaction rims separate rounded and sometimes sector-zoned cordierite porphyroblasts from the dark irregularly banded slaty matrix of this rock. Collected Dec 1832 - Feb 1833.
This collection was a collaboration between The Open University and the Sedgwick Museum, created in 2009 to celebrate the bicentennial of the birth of Charles Darwin.
The Sedgwick Museum opened a new gallery, 'Darwin the Geologist', and created a museum-based virtual microscope to showcase rocks he collected during the Voyage of the Beagle. We enjoy this collection because Darwin did not always pick up a representative sample from the islands he visited; it's often the unusual rocks that caught his eye. Just explore the collection and you'll see what we mean. For those who have the opportunity, a visit to the museum is strongly recommended.