DUFRENOYSITE, BAUMHAUERITE with REALGAR (micro and miniature)

A very rare and older specimen from the Lengenbach Quarry.

Dufrénoysite is a rare mineral classified within the sulfides and sulfosalts group, characterized by its chemical formula Pb2As2S5, which categorizes it as a lead sulfarsenite. This mineral crystallizes in the monoclinic system, forming large, longitudinally striped crystals that typically exhibit a tabular shape, though needle-like forms are occasionally found. Its surfaces display a metallic luster, and the mineral ranges from faintly translucent to opaque, presenting a lead to steel-grey hue with streaks of reddish-brown to chocolate-brown.

Dufrénoysite was first identified in the Lengenbach pit located in the Binn Valley of Switzerland's Valais canton. The mineral was described in 1845 by Augustin Alexis Damour, who named it in honor of the French geologist and mineralogist Armand Dufrénoy. In 1864, Julius Berendes further explored the properties of this mineral in his dissertation.

Baumhauerite (Pb3As4S9) is a rare sulfosalt mineral composed of lead, characterized by its triclinic crystal system and a color range from gray-black to blue-gray, exhibiting a metallic to dull luster. With a hardness rating of 3, it typically forms small crystals found within dolomitic marble. This mineral is predominantly located in the Lengenbach Quarry in the Valais region of Switzerland, where it was first discovered by the German mineralogist Heinrich Adolph Baumhauer in 1902. Lengenbach is renowned among mineralogists for its diverse collection of rare minerals. Additionally, Baumhauerite has been identified at Sterling Hill in New Jersey, USA, often in conjunction with molybdenite, and in aggregate forms at Hemlo in Thunder Bay, Ontario, Canada.