Subsequently, he became distinguished for his researches on mineralogy and crystallography. He was the author of Essai de Cristallographie (1772), the second edition of which, regarded as his principal work, was published as Cristallographie (3 vols. and atlas, 1783).[2][1] His formulation of the Law of Constancy of Interfacial Angles built on observations by the geologist Nicolaus Steno.[citation needed]