COLORADO FERBERITE AND THE WOLFRAMITE SERIES. 19 



CRYSTAIililZED FERBERITE. 



As has been stated, the ferbmti' commonly orrur> in d< 



crystal forms and the beauCy of the crystals is unique. However, 

 although crystals are common, good specimens suitable for display 

 in museums are very rare, for most of the crystals are so small that 

 they appear insignificant; they are very fragile and are easily broken 

 in mining; and in many places they arc coated with mixtures of 

 chalcedony, opal, and hydrous iron oxides in varying proportion-. 

 This coating may be removed from some specimens without serious 

 injury by treatment with hydrofluoric and sulphuric acids, but 

 crystals so treated show uneven surfaces when an attempt is made 

 to measure them with a goniometer. 



Probably a wedge shape is the commonest form of the crystals. 



lis form occurs in many of the mines. One of the best specimens 

 seen is from the Hoosier mine, between 1 and 2 miles northeast of 

 Nederland (PL VII, B] . The wedge shapes are formed by the termina- 

 tions at the ends of the b axis and most of the crystals are attached 

 at one end of this axis. Some crystals are intergrown in such a way 

 as to produce a fan shape (PL \ 7 TI, A and B). In a few specimens 

 crystals attached by one end of the c axis are prominent, in which 

 case the termination at each end of the b axis is shown. Some of the 

 crystals show penetration twins, extending through c{001}. Around 

 the penetrating crystal in two or three occurrences there seem to be 

 reentrant angles hi the penetrated members (PL VIII, A). The speci- 

 men illustrated came from a tract of land known as the Crow patent, 

 near Nederland. 



In a specimen from the Georgia A. claim the crystals are ^Imost 

 jgujjjc^and about one one-hundredth inch (0.25 millimeter) across. 

 Plate VIII, B, represents the specimen magnified 10 diameters. 



Another form of crystal is found on the Nugget and the Winnebago 

 claims, near Rollinsville, Gilpin County. In this form the crystal 

 presents a face (b) which is a long, narrow rhomb, with a length of 

 about three-eighths inch (9.4 millimeters) and a width one-tenth 

 to one-fifth as much. Typical specimens are shown in Plates IX and 

 X. In some specimens the rhomb has sides much more nearly 

 of equal length. (See PL XI.) Plate XII shows a very fine speci- 

 men with peculiar, irregular faces. The crystal forms are described 

 at length by W. T. Schaller in the latter part of this bulletin. 



COMPOSITION OF FERBERITE AND OTHER MEMBERS 

 OF THE WOLFRAMITE SERIES. 



The original ferberite was found in the Sierra Almagrera, in southern 

 Spain, and is stated by Liebe 1 to have been named by Breithaupt 

 Tor R. Ferber, of Gera. Liebe made an analysis" of the mineral. 

 (See"analysis No. 79, pp. 32-33.) 



i Liebe, K.L.H., Ein neuer Wolframite, ein Beitrag zu Mineral Chemie: Neues Jahrb., 1863, pp. 540-563. 



