The date and place of her birth cannot be fixed with accuracy; but, as a memoir published in 1640 says that for thirty years she had been engaged in mineralogical studies, it seems probable that she was born about 1590. She belonged to the noble family of Bertereau, in the Touraine; her Christian name was Martine. In 1610 she married Jean du Châtelet, Baron de Beausoleil and d’Auffenbach, a Brabantine nobleman of great learning and abilities. The Baron had borne arms in his youth, but his natural tastes lay in the direction of natural philosophy, and his attention was chiefly directed to mineralogy, then a science in its earliest infancy. Following the bent of his inclinations, and impelled by the desire of obtaining a practical acquaintance with the working of mines, and the character and conditions of the different metal ores _in situ_, he visited in order the mines of Germany, Hungary, Bohemia, Tyrol, Silesia, Moravia, Poland, Sweden, Italy, Spain, Scotland, and England. By this means he obtained a practical knowledge of his subject possessed by no other in his day, and an intimate acquaintance with ores and their indications, which made him the first of mineralogists. The German Emperors, Rudolph and Matthias, recognised his abilities, and constituted him Commissary-General of the Hungarian mines. The Archduke Leopold created him Director-in-Chief of the Trentin and Tyrolean mines, and the Dukes of Bavaria, Nieubourg, and Cleves conferred upon him similar offices in their territories; lastly, a brevet of like nature was given him by the Pope for the States of the Church. In 1600, at the recommendation of Pierre de Beringhen, Controller-General of the French mines, the Baron came to France. Ten years after he married Martine de Bertereau, who thenceforth became his companion in all his travels, his fellow-labourer in the same field of science, and who even surpassed him in ability and skill in detecting the indications of ore. The couple examined together the German, Italian, and Swedish mines. She then crossed the Atlantic to investigate those of the New World. She next applied herself to the study of chemistry, geometry, hydraulics, and mechanics, and became accomplished in each of these sciences. She was able to speak fluently Italian, German, English, Spanish, French, and was a Latin and Hebrew scholar. In 1626, Cinq-Mars, then superintendent of the mines, gave the Baron a commission to traverse several of the provinces, and open mines wherever he found indications of ore. Whilst thus engaged, the Baron published a volume on _The True Philosophy concerning the First Matter of Minerals_, a work of no great value, as it is overloaded with the absurd theories of the metamorphosis of metals then in vogue.