Darwin wrote "Compact greenish grey lava, with many small crystals of glassy feldspar (Basis finely crystalline)"
Trachyte dominated by a flow-banded groundmass of aligned anorthoclase feldspar crystals. Phenocryst species include irregularly twinned oligoclase-anorthoclase, pyroxene (augite), and less common green amphibole (hastingsite), olivine and magnetite. Collected Sept-Oct 1835.
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.