Emil Wilhelm Cohen (12 October 1842 – 13 April 1905) was a German mineralogist and petrographer, born in Jutland.

Cohen devoted his following years to mineralogy and drafting descriptions of his African explorations.

Through his Sammlung von Mikrophotographien zur Veranschaulichung der mikroskopischen Structur von Mineralien und Gesteinen] (1881–83; "Collection of Microphotographs on the microscopic Structure of Minerals and Rocks"),[1] he founded modern petrography.

In 1878 Cohen became professor of petrography at Strasbourg and Director of the Geological Survey for Alsace and Lorraine.

Beside detecting diamonds, he isolated and analyzed an iron carbide mineral there, later named Cohenite for him.