400 C. Palache and II. E. Merwin — Alamosite. 



from individual crystals. The high luster of the mineral, 

 however, made it possible to obtain readings from the most 

 minute faces and fairly consistent measurements were finally 

 obtained from six crystals. 



Alamosite is monoclinic, the fibers elongated parallel to the 

 axis of symmetry (crystallographic axis b). This habit and 

 the minute size of the crystals made it necessary to mount 

 them on the two-circle goniometer with 010 as pole and the 

 orthodome zone as prism ; the measurements and calculated 

 angle§ of the table are, therefore, given for that position, but 

 the symbols and axial ratio are for the normal position. The 

 position was chosen so as to bring out as well as might be, the 

 relation in form to wollastonite. 



The crystals are simple showing the forms <?(001), $(100), 

 6(010), w&(110), tf(101), (7(011) i?(121), and r(121). The figure 

 shows a typical combination in which the forms named, except 

 m and r, are represented in about their normal development. 

 The relations to wollastonite are shown by the following 

 angles : 



Axial Ratio 



Alamosite Wollastonite 



a : b : c a : b : c 



1-375 : 1 : 0'924 1-053 : 1 : 0-967 



Angle 001 to" 100=0 84°10' 84°30' 



" 001 to 101 32 02 40 03 



" 001 to 011 42 36 43 55 



" 100 to 110 53 50 46 21 



Table of calculated and observed angles of alamosite, with 

 010 as pole and 100 as first meridian. 



Elements for this position : ^ = 1*088 ; q = 0'731 ; / u=84°10' 



Elements for normal position : ^> =0 # 672; ^=0-919; fx=84 10 





Calculated 







Measured (m< 



san) 



No. o: 







i 



£ 





9 



< 



£ 



J 



o 





c 



001 



84' 



3 10' 



90 



D 00' 



84 ( 



D 10' 



90' 



w 



8 



a 



100 



00 



00 



90 



00 



00 



00 



90 



00 



6 



b 



010 



00 



00 



00 



00 



00 



00 



00 



00 



6 



m 



110 



00 



00 



36 



10 



00 



00 



36 



00 



1 



V 



101 



52 



08 



90 



00 



51 



53 



90 



00 



3 



9 



011 



84 



10 



47 



24 



84 



10 



47 



29 



6 



P 



121- 



-60 



11 



31 



57 



— 60 



12 



31 



58 



9 



r 



121 



52 



03 



34 



25 



52 



10 



34 



18 



2 



Physical Properties: — Cleavage perfect parallel to 010, 

 therefore across the fibers. Specific gravity 6*488 ±'003, 

 determined in the pycnometer on *6 CC of mineral (Merwin). 

 Hardness 4-5. Luster adamantine. Plane of the optic axes 



