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Esper S. Larsen, Jr.

Esper Signius Larsen, Jr. was born in Astoria, Oregon on March 14, 1879, the son of the first Danish Consul to be stationed in Portland, Oregon. Following graduation from high school in 1898, he spent the next four years working in a grocery store to accumulate enough money to attend college. In 1902 he enrolled at the University of California, and had originally intended to study mining engineering; but through the influence of A. C. Lawson and A. S. Eakle his attention turned to mineralogy and petrology. Remaining as an instructor after his graduation in 1906, he was soon promoted to acting professor of geology. He joined the U.S. Geological Survey in 1909, and after receiving his PhD in 1918 he was placed in charge of the petrology section.

Larsen was an early proponent of the immersion method for determining the optical characteristics of tiny mineral grains under the petrographic microscope. He set himself the task of determining the optical constants of all available, valid (transparent) species—600 of them—and after years of work he finally published "The microscopic determination of the non-opaque minerals" in 1921; this classic work, and its second edition of 1934, were used by every student of mineralogy throughout the world, and made the petrographic microscope an indispensable tool in mineral characterization.

Larsen joined the faculty at Harvard University in 1923, published seminal works on the geology of the San Juan Mountains in Colorado and the Highwood Mountains in Montana. He developed the lead-uranium isotope age-dating method, and authored or co-authored the descriptions of 24 new mineral species, including seven from Fairfield, Utah. His 1930 paper with Earl V. Shannon ("Minerals of the phosphate nodules from near Fairfield, Utah") was the first comprehensive description of the mineralogy of that occurrence. In total he published 130 professional papers, and many of his students went on to distinguished careers in mineralogy and geology.

Gentle, thoughtful, kind and absent-minded, Larsen was well loved and appreciated by his students. He married Eva Audrey Smith (daughter of a Member of the U.S. House of Representatives from California) in 1910, and they had two children: Clark Smith Larson (who died prematurely at age 36) and Esper Signius Larsen III (1912-1961) who, following in his father's footsteps, became a petrographer with the U.S. Geological Survey (Hurlbut, 1962). Esper S. Larsen died March 8, 1961.

BUDDINGTON, A. F. (1964) Esper Signius Larsen, Jr. 1879-1961. Biographical Memoirs of the National Academy of Sciences, 161-184.
HURLBUT, C. S. (1962) Memorial of Esper Signius Larsen, Jr. American Mineralogist, 47, 450-459.
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