Editing Nicolas Steno (section)

=== Crystallography ===
{{further|topic=crystallographic indices|Crystal system}}
Steensen gave the first accurate observations on a type of crystal in his 1669 book ''De solido intra solidum naturaliter contento'' (the ''Dissertationis prodromus'').{{sfnp|Kunz|1918}} The principle in [[crystallography]], known simply as ''Steensen's law'', or the [[law of constancy of interfacial angles]] or the ''first law of crystallography'',<ref>{{cite journal | last1 = Molčanov | first1 = K. | last2 = Stilinović | first2 = V. | year = 2014 | title = Chemical Crystallography before X-ray Diffraction | journal = Angew. Chem. Int. Ed. | volume = 53 | issue = 3| pages = 638–652 | doi = 10.1002/anie.201301319 | pmid = 24065378 }}</ref> states that the angles between corresponding faces on crystals are the same for all specimens of the same mineral. Steensen's seminal work paved the way for the [[law of rational indices]] of French mineralogist [[René-Just Haüy]] in 1801.{{sfnp|Kunz|1918}}<ref>{{cite web |title=Stephen A. Nelson (Tulane University) Introduction to Earth Materials |url=http://www.tulane.edu/~sanelson/eens211/introsymmetry.pdf |access-date=11 January 2012}}</ref> This fundamental breakthrough formed the basis of all subsequent inquiries into [[crystal structure]].