William Barlow (geologist)

William Barlow (1845 – 1934) was a British crystallographer and mineralogist who made significant contributions to the understanding of crystal structure. He is best known for his early theoretical models of crystal structures, developed before the advent of X-ray diffraction techniques.

Barlow, largely self-taught in mathematics and crystallography, deduced possible arrangements of atoms in crystals based on packing considerations and the chemical composition of the minerals. He proposed models for several common crystal structures, including those of sodium chloride (NaCl) and diamond, remarkably accurately anticipating the results that would later be confirmed by X-ray crystallography.

His approach involved visualizing atoms as spheres and meticulously investigating how these spheres could be packed together to fill space in the most efficient and symmetrical way. He categorized these packings and related them to observed crystal habits.

Barlow published his ideas primarily in the 1880s and 1890s. While his work was initially met with skepticism due to the lack of experimental verification, the later development of X-ray diffraction by Max von Laue and William Henry Bragg and William Lawrence Bragg provided conclusive evidence supporting many of Barlow's structural models. His insights proved crucial to the development of modern crystallography.

He was elected a Fellow of the Royal Society in 1909.