21 



Crystal 4 (Fig. 4, Plate I) is a less distinct fragment (the top 

 end) of a left-handed crystal. It shows the following forms : 



ш = {10Т0}, r = {lOri}, ^ = {OlTl}, 5 = {2Ги}, 7г = {0П2}, 

 and (с) = {Г545}. 



On the top all the three faces of the form tz occur compa- 

 ratively large. The form (c) has not, as far as I know , been 

 observed before on quartz. It occurs as a negative right tra- 

 pezohedron with two rather large faces. Also on crystal 3 it 

 is represented by a narrow plane. It is remarkable, however, 

 that on crystal 4 this form is represented as a left trapezohedron 

 by one face. The crystal is probably not a twin ; and it may, 

 therefore, be supposed that both the right- and the left-handed 

 forms occur. The faces are not, however, quite even; but 

 they cannot be regarded as solution planes, because the crystal 

 fragment shows no other traces of etching. The indices have 

 been calculated from the following angular value : 



Measured. Calculated. 



To45 : Oni = 8° 58' ^"^ W. 



The forms found on quartz from Narsarsuk are therefore 

 the following. 



ш={10Го}, r = {lOn}, г ={2021}, i¥={303l}, Б={8081}, 



^ = {OlTl}, 7г = {01Г2}, .s = {2TTï}, î)={718l}, 



[a) = {21. 9. 12. 7}, and (с) = {Т54б}., 



The above lines contain an account of the occurrence of 

 quartz on Narsarsuk partly massive filling the spaces between 

 crystals of other minerals, and partly in regularly developed cry- 

 stals. But the mineral occurs also in a third form , which is 

 perhaps the most common, namely in individuals that have been 

 so strongly attacked by solvents that one can no longer see 

 whether they were originally idiomorphic crystals or massive 

 lumps. The quartz crystals from Narsarsuk show all the 

 stages of etching , from its appearance as a mere trace to the 



