Darwin wrote "Imperfect gneiss or mica slate at junction of granite & clay slate on Lion's Back. (Layers very thin; scales of mica small, layers slightly contorted; mica black, glittering; feldspar granular, yellowish; quartz in small quantity, very thin laminae, but perfectly characterized, mixed with coarse granitic veins, if indeed they are veins and not parallel layers)"
This section shows the contact of a biotite-rich schist (top left) with altered, coarsely-crystalline biotite granite. Large crystals of plagioclase feldspar are partially replaced by sericitic mica. Quartz in the sample has been indurated with carborundum during sample preparation. Collected May-June 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.