Karl Ludwig Felix Machatschki (22 September 1895 – 17 February 1970) was an Austrian mineralogist. He was born in Arnsfeld near Leibnitz in Styria, Austria. He studied at the University of Graz, finishing his habilitation in 1925; in 1927 he joined the group of Victor Goldschmidt in Oslo for one year.
In 1930 he was appointed as a professor at the University of Tübingen. He changed university twice, first in 1941 to the University of Munich and finally in 1944 to the University of Vienna.
His scientific work created the basis of general mineralogy and crystal chemistry.