Franz-Joseph Müller, Freiherr von Reichenstein or Franz-Joseph Müller von Reichenstein (1 July 1740 or 4 October 1742 – 12 October 1825 or 1826) was an Austrian mineralogist and mining engineer. Müller held several positions in the Habsburg monarchy administration of mines and coinage in the Banat, Transylvania, and Tyrol. During his time in Transylvania he discovered tellurium in 1782. In his later career he became a member of the imperial council in Vienna and was knighted and elevated to the rank Freiherr in 1820. Place and date of birth Müller was born in 1740 or 1742 in the Habsburg Empire. While the Allgemeine Deutsche Biographie gives 1 July 1740 and Vienna as date and place of birth, the Neue Deutsche Biographie prefers 4 October 1742 and the small town of Poysdorf in Lower Austria. The much older works Neuer Nekrolog der Deutschen and Oesterreichische National-Encyklopädie do not give a place of birth and only the year 1740 for his birth. Even articles by Mary Elvira Weeks on the discovery of tellurium, published in the Journal of Chemical Education in 1932, and 1935 quote two different locations of his birth: one in Vienna, Archduchy of Austria and the other Hermannstadt, Principality of Transylvania (present-day Sibiu, Romania). A newer biography on the topic makes clear that date and place of birth are not definitely known. Education and career He studied philosophy and law in Vienna. After finishing his studies he started further studies at the Bergakademie (Mining Academy) in Schemnitz (Selmecbánya), Lower Hungary (today Banská Štiavnica, Slovakia) in 1763. He studied mining, mechanics, mineralogy and chemistry and after graduating he became a Markscheider (official mine surveyor) in 1768. In 1770 he joined the Hofcommission für die Regulierung der Banater Berg und Hüttenwerke (royal commission for mining in the Banat) where he gained a lot of knowledge on mining in the Banat. He was promoted to the rank of an Oberbergmeister (senior mining official) and became a mine manager in the same year. In 1775 he became Oberbergmeister in the Tyrol town of Schwaz. Schwaz was one of the largest centres of silver and copper mining in Austria-Hungary in that time. In 1778 he discovered an occurrence of tourmaline in the Zillertal. Müller became one of seven Thesaurariats councillor in Transylvania responsible for the supervision of all mining and coinage activities in Transylvania in 1778. After the dissolution of the Thesaurariat Müller became