Further reading:
Darwin's rock collection:
https://www.virtualmicroscope.org/content/charles-darwins-rocks?fbclid=IwY2xjawUV36RwZG9mBWV4dG4DYWVtAjEwAGJyaWQRMEFXR3g2T0RadERTU0xDZkVzcnRjBmFwcF9pZBAyMjIwMzkxNzg4MjAwODkyAAEeC6thBY7a--93OxAa1PmMw1HpsMvKuN4HeDWESjcRJakb8UrwD9UAGyvnOfI_aem_1WF_P6t68kh8JMgV60ldSQ