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Geometry in unlikely places

"These bladder stones are most likely made up of calcium oxalate; they are faceted because they rub against each other. (Faceting only occurs when there are two or more stones together)".
Deductions from smooth rocks

Extract from Bettie Higgs's reading of rocks in 'Visual Practices Across the University'. Most of the rocks in this photograph are about 360 million years old, so the grains that comprise them are substantially older. The grains came originally from a mountain range, as large as the Himalayas, whose roots can still be seen in counties Mayo and Donegal, in the northwest of Ireland. The grains were carried south by rivers and deposited in this area; the smallest grains were carried all the way to the ocean, which was far south of Cork at the time, in what is now the Atlantic Ocean south of Ireland. (There was very little rainfall at the time: the portion of land that is now Cork was 10° south of the Equator. This can be deduced from the properties of the iron in the rock.) The water in which the grains were transported was oxygenated, and the iron precipitated out as iron oxide (haematite), which cemented the grains and which accounts for the red color (Elkins 2007: 74 - 78).