512 Hidden and Penfield—Hamlinite from Stoneha?n, Me. 



mineralogists of the occurrence of a probably new rhombohe- 

 dral mineral, requesting them to examine the specimens in 

 their own collections, but as up to the present time no success 

 has attended our efforts we feel warranted in giving as com- 

 plete a description as possible of the material in hand. We hope 

 that in the future sufficient material may be obtained for a 

 complete chemical investigation. We shall, moreover, con- 

 sider it a great favor if the readers of this article will carefully 

 examine the specimens of herderite which may be in their pos- 

 session and aid us in securing the necessary material. 



The system of crystallization is hexagonal-rhombohedral. 

 The crystals vary from one to two millimeters in diameter and 

 are quite flat from the predominance of the basal pinacoid. 

 They exhibit the forms e, 0001, O ; r, 1010, 1 and f 0221,-2, 

 which are developed as shown in the accompanying figure. 

 All of the planes are more or less uneven, especially r, which 

 always yielded a number of reflections ; 



of the signal, so that it was quite im- r -~~~cl.....~*p ^ 



possible to obtain accurate measure- vT .--'' jJ^\ 

 ments from them. The angle which \*\ 7 r / h 



was selected as fundamental was f ^ f, \ ^----- ^^-^ :: ^ > / 

 2201 a 0221 = 108° 2' from which the >~ / ^ 



length of the vertical axis c = 1*135 was calculated. 



Other measurements resulted as follows : 





Measured. 



Calculated, 



r /s r, 



lOll ~ 0111 = 



87° 2' 



c /«. r, 



0001 >s 1011 = about 55° 



52° 40' 



c */» 



0001 a 0221 = 69° 15' — 70° 30' 



69° 7£' 



/ a r, 



0221 * 1011 - 53° 35' - 54° 27' 



54° V 



The. cleavage is perfect parallel to the base. The luster on 

 the basal plane is pearly and on the rhombohedral faces is greasy 

 vitreous, very similar to that of herderite. Some of the crystals 

 are transparent and colorless, others show a faint yellow tint, 

 owing probably to some impurity. Crystals lying on a basal 

 plane, when examined under the microscope in convergent pol- 

 arized light, show a perfectly normal, uniaxial interference fig- 

 ure, with positive and not very strong double refraction. 



The hardness is 4*5. Specific gravity taken with the barium - 

 mercuric iodide solution was 3*228. 



Before the blowpipe the mineral fuses at about 4 to a white 

 porcelain-like mass, coloring the flame pale green (P 2 & ). In 

 the closed tube it gives abundant water which is strongly acid 

 and etches the glass (F). It is slowly soluble in acids and gives 

 with ammonium molybdate a strong P 2 6 reaction. With H 2 S0 4 

 it gives no micro-chemical reaction for Ca. The presence of 

 P a 6 interfered with making the ordinary micro-chemical reac- 



