Eskola, Pentti Elias

(b. Lellainen, Honkilahti, Finland, 8 January 1883; d. Helsinki, Finland, 6 December 1964)

petrology, mineralogy, geology.

The son of a farmer, Eskola enrolled at the University of Helsinki in 1901 and in 1906 obtained his candidate degree (about equivalent to an M.S.) in chemistry. He obtained his Ph.D. at the same university in 1914 with a dissertation entitled “On the Petrology of the Orijärvi Region in Southwestern Finland.” By 1915 he had embarked on his lifework, the study of the mineral facies of rocks. During stays in Norway and the United States in 1920–1921 he worked specifically on eclogites; he spent 1922–1924 as a geologist of the Finnish Survey; and in 1924 he was named extraordinary professor and in 1928 ordinary professor of geology at the University of Helsinki, a position he held until 1953. Eskola was one of the generation of petrologists confronted by the complexities of the Fennoscandian crystalline complex who were inspired by a famous paper of J. J. Sederholm on granites and gneiss to develop a structural-metasomatic school of petrology, influenced also by the application to petrology of physical chemistry by J. H. L. and T. Vogt.

Eskola was a leading petrologist in these and other subjects (mentioned below), within his own field. He held honorary degrees from the universities of Oslo (1938), Padua (1942), Bonn (1943), and Prague (1948). He was honorary president of the Geological Society of Finland and an honorary or corresponding member of many learned societies and academies of science. In 1964 he received the Vetlesen Prize.

Eskola married Mandi Wiiro in 1914. They had two children; a son, Matti, born in 1916 and killed in World War II in 1941; and a daughter, Päivätär, born in 1920, who became a teacher of chemistry. Eskola and his wife were known for their warmth and cooperation in the scientific and personal care of their students, many of whom held important positions in Finland and abroad.

The success of Eskola’s scientific work was probably based on the coincidence of three major factors: his thoroughness and steadiness, evident in all his writings and his notable care in rewriting manuscripts; the breadth of his topical experience, including his degree in chemistry, displayed not only in his specific papers but also, especially, in his various textbooks in geology and mineralogy, some of which were written in German; and his constant striving to combine laboratory results with field data, evident in his work in chemistry, his stay at the Geophysical Laboratory in Washington from March 1921 to November 1922, his own fieldwork, and his published work.

Eskola’s major contribution to the earth sciences and an idea that he developed throughout his life—indeed, from his first work on solid-state reactions in 1904 to his last years—was the concept of mineral facies, essentially a continuation of Ulrich Grubenmann’s assignment of metamorphic rocks to epi-, meso-, and katazones. In 1914 he wrote on p. 114 of his Ph.D. thesis a definition that is still applicable today: “In any rock of a metamorphic formation which has arrived at a chemical equilibrium through metamorphism at constant temperature and pressure conditions, the mineral composition is controlled only by the chemical composition.” Originally he differentiated between five separate facies, stressing their independence of mode of formation. He named them, according to a mineral typical of each, the sanidine, hornfels, greenschist, amphibolite, and eclogite facies. By 1939 in Die Entstehung der Gesteine this nomenclature had evolved into a two-dimensional temperature-pressure classification further differentiated into metamorphic and magmatic facies. An early summary of this basic idea was published in 1920 under the title “On Mineral Facies of Rocks” (Norsk geologist tidsskrift, 6 , 143–194).

Through his own work and that of many other colleagues—specifically Paul Niggli, V. M. Goldschmidt, T. F. W. Barth, F. J. Turner, N. L. Bowen, and H. Yoder—the equilibrium boundaries and stability fields were increasingly specified and modified, until after 1955 an intensive search for new metamorphic facies standards began on a grand scale. As a corollary, Eskola centered repeated efforts on the highest-grade facies, the eclogite problem. An introductory account is his paper “On the Eclogites of Norway” (Skrifter utg. of Videnskabsselskabet i Kristiania, 1 , no. 8 [1921]). The modern concept that deeper layers of the earth do not necessarily differ in composition but rather in the density of their minerals largely originated in Eskola’s high-pressure facies idea.

As in his early work on the petrology of Orijärvi, he often interpreted the composition of his mineral facies as the result of metasomatism, specifically of a “replacement of lime, soda, and potash by iron oxides and magnesia.” Eskola originally considered the intrusion of granites to be principally responsible for such ionic migrations but was open to a later interpretation by some of his students who derived the same elements from a process of metamorphic differentiations and tectonic energies. A syngenetic interpretation (in situ formation) favored more recently by some ore geneticists seems not to have been considered during Eskola’s lifetime.

The problem of the origin of metamorphic rocks is indigenous to the geology of Finland. Likewise, the granite problem is a typical Fennoscandian study, and it consequently received almost as much attention from Eskola as the metamorphic rock enigmas. As early as 1932 he summarized his ideas on granites in a paper entitled “On the Origin of Granitic Magmas.” He recognized various possible origins, including anatectic processes by which a “pore magma” may form and migrate to produce migmatites. In his later years he agreed that palingenesis or anatexis may have played a more important role than was recognized at first; but he did not share the extreme interpretations of some transformist schools.

Because the problems mentioned so far could be investigated largely through work in Scandinavia, Eskola’s contributions to the advancement of Fennoscandian geology were numerous. He was particularly active in the interpretation of pre-Cambrian stratigraphy; for example, the term “Karelian” goes back to his work. In connection with this work, and as a man with a thorough philosophical mind, in 1954 he also presented a book on the possible cosmogenic origin of the earth and of life (In Quest of a Picture of the World).

BIBLIOGRAPHY

I. Original Works. From a list of about 170 original publications (articles, books, and monographs), the following perhaps best represent Eskola’s lifework: “The Silicates of Strontium and Barium,” in American Journal of Science, 4 (1922), 331–375; “On the Origin of Granitic Magmas,” in Mineralogische and petrographische Mitteilungen, n.s. 42 (1932), 455–481; “Wie ist die Anordnung der äusseren Erdsphären nach der Dichte zustande gekommen?,” in Geologische Rundschau, 27 (1936); 61–72; “Die metamorphem Gesteine,” in T. F. W. Barth, Carl W. Correns, and Pentti Eskola, Die Entstehung der Gesteine; Ein Lehrbuch der Petrogenese (Berlin, 1939; repr., 1960), pp. 263–407; “Einführung, ‘Finnlandheft der geologischen Rundschau,’” in Geologische Rundschau, 32 (1941), 401–414; “Kern und Schicten der Erde,” in Sitzungsberichte der Finnischen Akademie der Wissenschaften (1945), 218–228 (Finnish ed. 1946); Krristalle und Gesteine. Ein Lehrbuch der Kristallkunde and allgemeine Minerlagoie (Finnish ed. 1939; repr. Vienna, 1946); “About the Granite,” in Comptes rendus de la Sociéte géologique de Finlande, 28 (1955), 117–130, also in Bulletin de la Commission géologique de la Finlande, 168 (1955), 117–130; “On the Mineral Facies of Charnockites,” in Journal of the Madras University, 27 (1957), 101–119; and “Granitentstehung bei Orogeneses und Epriogenese,” in Geologische Rundschau, 50 (1960), 105–133.

II. Secondary Literature. On Eskola and his work, see T. F. W. Barth, “Memorial to Pentti Eskola (1883–1964),” in Bulletin of the Geological Society of America, 76 no. 9, 117–120; Vladi Marino, “Pentti Eskola,” in Bulletin de la Commission géologique de la Finlande, 218 (1965), 20–53; Toini Mikkola, “Memorial of Pentti Eskola,” in American Mineralogist, 53 544–548; and T. G. Sahama, “Pentti Eskola,” memorial address given in Helsinki, 10 November 1965.

G. C. Amstutz