Aubrecht, R., C. Brewer-Carías, B. Šmída, M. Audy & Ľ. Kováčik (30 January 2008). Anatomy of biologically mediated opal speleothems in the World's largest sandstone cave: Cueva Charles Brewer, Chimantá Plateau, Venezuela. Sedimentary Geology203(3–4): 181–195. doi:10.1016/j.sedgeo.2007.10.005