438 Larsen and Hicks — Searlesite. a new mineral. 



The extinction angles vary from zero to very large. The 

 elongation is positive for libers showing zero or small extinction 

 angles. The mineral is probably monoclinic in crystal symme- 

 try. 



An attempt to dissolve out the calcite with dilute acids 

 revealed the fact that the optical properties of searlesite 

 gradually change on treatment with acids. The indices of 

 refraction decrease, the birefringence remains about the same, 

 the extinction becomes sensibly parallel, and the axial angle 

 smaller. A specimen treated with cold, dilute hydrochloric 

 acid for several hours showed the following optical properties : 



(3= 1*465 y-a='01 



Extinction parallel and elongation +. 



Another specimen treated for a shorter time showed : 



y = 1-480 a = 1-470 Optically — . 2E = rather large 



Extinction parallel and elongation + . A specimen treated 

 with acetic acid shows ft = 1-50-1*51. 



Chemical properties. — A sample of nearly 1*5 grams of the 

 spherulitic material was washed with 75 cc of water to remove 

 the admixed chlorides, dried at 100° C. and preserved for analy- 

 sis. Inasmuch as the sample contained large quantities of 

 calcite and considerable quartz and feldspar, besides smaller 

 amounts of other impurities, a method of analysis which would 

 eliminate as much of these impurities as possible was planned. 

 The carbon dioxide was determined on a half gram sample by 

 the usual gravimetric method. The material from this deter- 

 mination was digested on the steam bath with strong hydro- 

 chloric acid, filtered through a Munroe crucible, and the residue 

 thoroughly washed with water. The amorphous silica was 

 then extracted from the residue by hot ten per cent sodium 

 carbonate solution. The residue still remaining was acidified, 

 thoroughly washed with water, dried at 100° C, and weighed. 

 By microscopic examination this insoluble matter was found to 

 be composed largely of plagioclase with some microcline, 

 chlorite, quartz, hornblende, and clay. After ignition the 

 residue was weighed and reported as insoluble matter. The 

 silica was recovered from both the hydrochloric acid and the 

 sodium carbonate extracts and determined in the usual way. 

 After removing boric acid the rest of the analysis was accom- 

 plished by well-known methods, boric acid being determined 

 in a separate portion by distillation with methyl alcohol and 

 titration with standard sodium hydroxide in the presence of 

 mannitol. 



