ever presented in New Spain. He made important studies of minerals and developed innovative methods in mining. He also wrote the first textbook of mineralogy to be published anywhere in America, Elementos de Orictognosía, and the first in Spanish rather than German or English. Volume I appeared in 1795, and volume II in 1805. Santiago Ramírez, his student and later his biographer, described it as "a monumental work, which... will be an object of veneration and consultation". German naturalist, Alexander von Humboldt, making a survey of resources in Spanish-held colonies for Spain, reported favorably that it was in Mexico where the best work of mineralogy in Spanish had been published, the Elementos de Orictognosia of Señor Del Rio. Humboldt spent the period from March 1803 to March 1804 in Mexico City, renewing his friendship with del Rio and actively participating in the investigations of the College of Mining. He organized excursions to Chapultepec, to the basaltic zone of Pedregal de San Ángel, the lava fields of the Xitle volcano, and to the hot springs of Peñón de los Baños, a rocky outcrop close to the modern Mexico City International Airport, accumulating data and samples of minerals and rocks that were then submitted to chemical tests for identification. In 1820 del Río was named a deputy to the Spanish Cortes. He was a liberal who argued for the independence of New Spain. He was in Madrid when Mexico gained its independence. Invited to remain in Spain, he nevertheless returned to Mexico (in 1821), which he considered his homeland. In 1829, after the turbulent period of war with Spain, the government of independent Mexico expelled the Spaniards resident in the country, with some notable exceptions. Del Río was one of the exceptions. The expulsion had a major impact on the work of the College of Mining. The director, Fausto Elhúyar, was forced to resign and leave the country. Indignant over the expulsion of his colleagues, del Río showed solidarity by himself entering voluntary exile in Philadelphia for four years. There he was highly honored. He took part in the scientific activities of the American Philosophical Society (elected 1830) and was elected president of the Geological Society of Philadelphia. John Hurtel of Philadelphia published a new edition of del Rio's book in 1832. Del Rio returned to Mexico in 1834 and again occupied the chair of mineralogy at the college. He was also