Esper S. Larsen Jr.

Esper Signius Larsen Jr. was an American geologist and petrologist, born in 1879 in Astoria, Oregon, and died in 1961, who developed optical microscopy techniques for identifying and analyzing non-opaque minerals in thin section. A professor of petrology at Harvard University from 1923 to 1949 after earlier work with the United States Geological Survey and the Carnegie Institution, he also proposed a lead-uranium ratio approach to estimating the age of uranium-bearing minerals that became known as the Larsen method. The minerals esperite and larsenite were both named in his honor.