Darwin wrote "Dark greenish greenstone-like base, with four crystals of glassy feldspar"
Sanidine, a high temperature potassic feldspar exhibiting simple twinning is the most obvious mineral in this lava sample. In places sanidine crystals show alignment that indicates flow directions prior to consolidation. Brown amphibole, pyroxene and iron oxides are also present. Collected in July 1836.
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.