Darwin wrote "Compact, dark greenish basaltic-like rock, with numerous very minute grains of red olivine"
Alteration of this basaltic rock has converted original olivine microphenocrysts into reddish-orange iddingsite. Nepheline is an uncommon microphenocryst phase. A single large xenolith of feldspar-rich material and a calcite-filled vein are the other features of note. Collected in Nov 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.