52 



in this manner sometimes fill up tolerably large spaces between 

 crystals of other minerals. Such masses, several centimeters in 

 thickness have been met with ; they seldom inclose foreign 

 minerals. The small crystals are generally grown together so 

 as to form thin flat plates , which are aggregated in parallel 

 position, so that the whole forms a porous, schistose structure. 

 The consistency of the whole is so loose that it can easily 

 be crushed between the fingers. 



In colour ancylite varies somewhat. Its normal colour 

 is light yellow inclining to orange. Often the crystals are 

 brownish or greyish, sometimes quite resin -brown. The 

 small crystals that form crusts are generally of a yellowish 

 green or yellowish grey colour. The crystal faces, when they 

 are not dull, show a vitreous lustre; the fracture has a greasy 

 lustre. The mineral is only subtranslucent. 



Microscopical sections are colourless, but somewhat opaque. 

 With a high magnifying power this opacity is found to be 

 chiefly due to numerous ægirine needles that are imbedded in 

 the mineral mass. The section orientated parallel to the first 

 pinacoid (a) is bounded by the traces of the faces that form the 

 prism of the first order. It has, consequently, rhombic boun- 

 daries. The extinction is here diagonal, though not quite uniform, 

 and is somewhat undulating, which probably depends on the 

 spheroidal form of the crystals. In the conoscope this section 

 presents an interference figure with large axial angle (the obtuse 

 bisectrix). The section parallel to the second pinacoid [b) is 

 bounded by the traces of the faces that form the prism of the 

 second order and, consequently, also has rhombic boundaries. 

 The extinction directions lie diagonally, and an undulation like 

 that in the foregoing section is observable. The conoscope 

 shows an interference figure with a smaller axial angle (the 

 acute bisectrix); also here, however, the axes are not visible 

 within the field of the microscope. The section parallel to 

 the third pinacoid (c) is bounded by the middle edges of the 



