Knopf and Sehaller — Two New Boron Minerals. 325 



lite-pyroxene hornfels, which reacts chemically for chlorine. 

 It is clear from the parage nesis of paigeite that it represents 

 a fixation product of magmatic emissions rich in fluorine (and 

 chlorine), boron, and iron. 



Hulsite. 



Hulsite always occurs crystallized ; either as small crystals 

 about l mm diameter, or as large tabular masses, extending sev- 

 eral centimeters and showing the prismatic cleavage well devel- 

 oped. The crystals, while often complete, are always uneven, 

 and the faces dull and rough, so that no measurements could 

 be obtained from any of the natural faces. Inspection with 

 a hand lens shows that these crystals are often rectangular in 

 shape, and as hulsite is provisionally considered orthorhombic 

 these rectangular prisms consist of three pinacoids. Sometimes 

 the crystals are bounded by the prism faces, and the basal 

 pinacoid, though it is not always possible to decide whether 

 the prisms are natural crystal faces or those due to cleavage. 

 Often one pair of prism faces becomes much larger than the 

 other pair. The cleavage parallel to the prism is good and 

 measurements of three such cleavage angles gave the values : 



m /\ m'" = 57° 44,' 57° 38', 57° 33'. Average value, 57° 38'. 



Therefore assuming that hulsite is orthorhombic, the crystal- 

 lographic elements become 



a : b : c = -5501 : 1 : ? . 



Forms a {,100}, I {010}, c {001}, m {110}. 



The crystals are often twinned, one individual being turned 

 about 120° to the other, the two basal pinacoids remaining in 

 the same plane. The crystals are also often grouped in paral- 

 lel position, especially when the individual crystals are elon- 

 gated parallel to a prism face. The following photomicro- 

 graph shows the characteristic appearance of hulsite crystals 

 when grouped together (fig. 1). 



The color of the mineral is black, and when free from 

 enclosed magnetite has a greenish, brownish and sometimes a 

 reddish tinge. Many of the smaller ciwstals are covered with 

 a brownish coating, probably limonitic in character. Streak 

 black, luster submetallic, but on the pure mineral inclining 

 more to vitreous-like hornblende. Hardness about 3. Den- 

 sity 4/28. Cleavage good, j^rismatic m{110}. Readily solu- 

 ble in HC1 and HF, less so in other acids. Gives off water 

 in a closed tube and before the blowpipe fuses quietly to a 

 dull black slag and colors the flame slightly green. Gives a 



