316 Penfield — Chemical Composition of Hamlinite. 



In its chemical composition hamlinite holds a unique posi- 

 tion among minerals, as strontium and barium have never 

 before been observed as essential constituents of a phosphate 

 and this is the first time that a pyrophosphate has been recorded. 



Note concerning Bertrandite Crystals from Oxford County, Maine. 



2 Associated with the hamlinite just 



described there was one specimen show- 

 ing prismatic crystals averaging about 

 2 mm in length and l mm in diameter, which 

 proved to be the rare mineral bertrandite. 

 The habit is shown in the accompanying 

 figure and the forms are as follows : 



b, 010 



c, 001 

 /, 130 



e, 011 



e, 031 



k, 0-12-1 



The crystals are in reality twins, two 

 hemimorphic individuals being united by their basal planes, 

 and occasionally the line of twinning may be traced horizon- 

 tally across the a, f and b faces. The specific gravity was 

 found to be 2*571. The measured angles are given below, 

 together with the calculated values derived from the axial 

 ratio a:b:c = 0-56885 : 1 : 0-59T3. 



Measured. Calculated. 

 /"a/, 130 ^ 130 = 119° 20' 119° 16' 

 c/ve, 001 a011= 30 50 30 51 



Measured. Calculated. 

 c a e, 001^031 = 60° 50' 60° 50' 

 c*k, 001^0-12-1= 82 20 82 4 



In closing the author desires to express his thanks to Mr. 

 Cahn for calling his attention to this new occurrence of ham- 

 linite and bertrandite. 



Laboratory of Mineralogy and Petrography, 

 Sheffield Scientific School, May, 1897. 



