24 Dana and Wells — JS'eio mineral, Beryllonite. 



search for smoky quartz and a considerable quantity was ob- 

 tained, including one crystal weighing nearly 100 lbs. The 

 beryllonite, however, was overlooked, being not unnaturally 

 taken for colorless quartz. 



The early specimens, like those which have been obtained 

 since, were found either detached in the soil or occasionally 

 imbedded in a loosely coherent brecciated mass obviously not 

 the original matrix. The material in which the crystals and 

 fragments occur has evidently been derived from a granitic 

 vein, fragments of partly kaolinized feldspar, smoky quartz 

 crystals and other species to be mentioned being common. 

 The exploration thus far carried on, however, has not brought 

 to light the vein in an unaltered condition, although an appar- 

 ent vein 4 to 6 feet wide of decomposed material has been 

 found. The country rock is mica schist, which has been met 

 with at a number of points in the course of the excavations. 



The species which have been obtained from the same spot 

 associated with the new mineral, and which probably represent 

 its original associates in the vein are the feldspars, orthoclase 

 and albite, smoky quartz sometimes in large crystals, mica, also 

 columbite, cassiterite, beryl, apatite, triplite. The crystals 

 bear evidence of having been implanted upon the rock on one 

 side as if they had occurred in cavities rather than completely 

 embedded. Some specimens, however, retain the impressions 

 of surrounding minerals, probably mica. A single specimen is 

 implanted upon apatite and inclusions of apatite have been 

 noted. The chemical agencies which have kaolinized the feld- 

 spar have also left their mark on the beryllonite the surfaces of 

 which are often roughened or in some cases delicately etched. 



Crystalline form. — The specimens in hand are in large part 

 fragments of crystals, ranging from those presenting a surface 

 of an inch or two square and weighing 40 to 50 grams down to 

 the size of a pea. Well formed crystals are rare ; the largest is 

 somewhat more than an inch across. All the specimens show a 

 highly perfect basal cleavage (<?), yielding easily smooth lustrous 

 surfaces. Exactly at right angles to this (measured 90° 0' and 

 89° 59^') is a second cleavage somewhat interrupted and ob- 

 tained with a little difficulty ; the third pinacoidal cleavage is 

 faintly indicated in the rectangular form of some of the broken 

 fragments, and a fourth cleavage is sometimes distinct parallel 

 to a prism of 60°. Twins are common in which the twinning 

 plane is a prism also of sensibly 60°,* but it is found that the 

 twinning prism and the cleavage prism, though having nearly 



* When the preliminary notice was written, no material was at hand allowing 

 of exact measurement and it was assumed that of the two possible twinning 

 planes, the one present was probably also the cleavage prism ; this has since been 

 shown not to be the case, hence the change of position here adopted. 



