FERBERITE, QUARTZ, & ARSENOPYRITE

ABOUT THE SPECIMEN Beautifully balanced arrangement of large and highly lustrous ferberite, with a 7.5 cm quartz crystal set right to the side, with some of the ferberite visible through it. Sphalerite crystals are dotted along the faces of the quartz to give a dazzling accent, and there’s smaller crystals of quartz intergrown with lustrous arsenopyrite at the front. Together with these four minerals, one can also see growths of siderite all around the piece. This lovely Panasqueira specimen goes all the way back to the 60's or 70's, and is a fine representation of this combination. Ex. Kurt Hefendehl. VIDEO   MORE INFO Portugal's leading tungsten producer since 1898, Panasqueira exploits a dense network of subhorizontal ferberite-bearing quartz veins cutting steeply folded Hercynian Beira Schist above a buried granite cupola. Fluid inclusion work by Kelly and Rye (1979) established that mineralization occurred from NaCl-dominated brines well below their critical temperatures during the oxide-silicate stage at 280–320°C - conditions that concentrated iron and tungsten into the iron end-member of the wolframite series rather than the manganese-dominant huebnerite. Ferberite at Panasqueira occurs as lustrous, submetallic black bladed to spearhead-shaped crystals with sharp striated faces, typically perched upright on quartz, sometimes with arsenopyrite or fluorapatite association; the high volatile content of the vein system promoted open-cavity growth - the rotos miners encounter underground - which accounts for the exceptional crystal termination quality. The mine has produced specimens continuously for decades and remains active under Sojitz Corporation, meaning supply is genuinely ongoing rather than dependent on fixed old-stock. What Panasqueira ferberite lacks in rarity it compensates with consistent quality: the deposit holds the position of the world's definitive ferberite locality, a status unlikely to change.