(b. Mâcon, France, 4 February 1863; d. Paris, France, 16 March 1948)
mineralogy, petrology, geology.
Lacroix’s grandfather, Tony, and father Francisqu, were paris-trained pharmacists; his grandfather’s avocation was mineralogy. When he was twenty, Lacroix went to Paris to earn a pharmacist’s diploma. Concurrenty he attended courses in mineralogy at the Musé um d’Histoire Naturelle, where his advanced knowledge came to the attention of his professors, F. Fouqué and A. des Clozzeaux. Recognizing his interest and natural ability, they made funds acailable to enable him to visit classic localities and collectins in Europe. After receiving the diploma in pharmacy in 1887, Lacroix chose to follow mineralorg and was appointed assistant. to Fouqué, a post he held while earning his doctorate. He received it 31 May 1889 and then, having fulfilled Fouqué’s prerequisite, on 6 June married Catherine, eldest fo the Fouqué daughters. On 1 April 1893 Lacroix was named to succeed des Cloizeaux in the chair of mineralogy at the museum, a position he held until his official retirement on 1 October 1936. He continued a full schedule of work at his labratory, walking there each day until four before hsi death at the age of eithty-five.
Lacroix early realized the impoortance to research of an excellent mineral collection, and for fifty years one of his undeviating aims was to build up a systematic collection from around the world. As a corollary he encisaged an inventory. He drew on acquaintances made during his early travels for exchange of specimens; he asked French colleagues in other sciences to collect while abroad; even administrators of French colonies found themselves collecting for Lacroix. This was particularly true of General Joseph Gallieni and his officers on Madagascar, which had come under French rule in 1895; they received detailed instructions for nethodical collecting and resonded so effectively that Lacroix visited the island in 1911 and undertook the detailed study that led to the publication of Minéralogie de Madagascar, a three-colume mine of information that has been superseded. In like manner a systematic volcaic island of the South Pacific was completed and led to the recognition of two distinct petrologic domains characterized by mesocratic and melanocratic basalts.
Following in the footsteps of Fouqué, Lacroix made volcanology and colcanic rocks one fo his specialaties. These studies began in 1890; in May 1902 there was a major eruption on the French island of Martinique in the Caribbean. Appointed by the Académie des Sciences to head a mission to study the volcanism, Lacroix spent six months sending back a stream of letters which appeared in the vigorous exposition that he later puplished of the nuée ardente, or glowing cloud type of eruption, which he alone, of all the observers of Mt. Pelée, was perceptive enough to recognize as a newly observed phenomenon. First suggested by Fouqué in 173, on the basis of tales of earlier eruptions in the Azores, an eruption of that type had never witnessed by a scientist. Subsequent nuée ardente eruptions have been recorded on Martinique and in other active volcanic areas; and the term, in the French form, has been accepted and used throughout the world. Lacroix also derived new evidence on the origin and behavior of volcanic domes. The results of his observations and investigations are in the two-volume Lamontagne Pelée. On 11 January 1904, the Académie des Sciences elected Lacroix a member in recognition; his way of putting it was “Jesuis entré à l’Institut sous l“irresistible poussée d’unvolcan.”
But this was not only colvanie “poussée” to which Lacroix responded. Up to 1914 he was an eyewitness to outbursts of Vesuvius, which was then in almost constant eruption, of Etna, and of other volcanoes. His other travels were to study minerals in their natural settings in order to supplement his laboratory determinations. Lacroix had a broad interpretation of mineralogy, believing that the study of minerals should not be an end in itself but a means of learning their origins and relations to the rocks in which they occur, the structure of the rocks, and the entire terrain. Mineralogy as a point of union of chemistry, physics, mathematics, and natural history could make use of the techniques of those disciplines; but it should not be separated from geology or geophysics. Being on the scene when mineralogy was in transition from a purely descriptive to an interpretive science, Lacroix was a brilliant exponent of the new trend.
Lacroix was named secétarire perpetuel of the Académie des Sciences on 8 June 1914. A lucid writer and an able administrator, he was admirably suited for the post and gave it meticulous attention during his thirty-four-year tenure. He reorganized the secretariat, enriched the archives, and lent needed support to an inventory of scientific materials in Paris libraries. Giving full play to his interest in the history of science and scientists, and with a wealth of facts at hand, he produced a series of biographies of French scientists of the seventeenth and eighteenth centuries. Written in a clear, fluent narrative style, they rank with the best in literature.
A kindly man of simple tastes who shunned any from of ostentation, Lacroix had the gift of creating an aura of good will among his students and colleagues. La bienveillance, c’est quelque chose dans la vie des hommes,” were his won words.
I. Original Works. Lacroix wrote, either alone or with Colleagues, about 650 papers, which were published primarily in French scientific journals between 1879 and 1946. His larger monographs include Minéralogie de la France et de ses colonies, 5 vols. (Paris, 1893–1913); La montagne Pelée et ses éruptions (Paris, 1904); La montagne Pelée après ses éruptions... (Paris, 1908); Minéralogie de Madagascar, 3 vols. (Paris, 1922–1923); Figures de savants, 4 vols. (Paris, 1932–1938); and Le volcan actif de l’ile de la Réuntion et ses produits (Paris, 1936), with supp. (1938).
II. Secondary Literature. At least twenty-two biographies of Lacroix have appeared in the scientific journals of several European countries and of the United States. A bibliography of 16 is in Bulletin de la Société françcaise de minéralogie et de cristallographie, 73 (1950), 408.