Penfield and Foote — Clinoltedrite. 293 



Theory for 



I. II. Average. Ratio. H 2 CaZnSi0 5 . 



Si0 2 27*14 27-29 27'22 "454 0-97 27'92 



ZnO 37*43 37-46 37'44 -462 ) ... Q • 37*67 



MnO ..... -49 -50 '50 -007 [ 469 1 °° 



CaO 26-31 26-19 26-25 -469 ) v 26-04 



MgO -07 -08 -07 -002 j 4/i 



H 2 8-53 8-59 8-56 -476 1-01 8*37 



(Fe.Al) 2 3 -26 -31 -28 



100-32 100-00 



The ratio of Si0 2 : (Zn+Mn)0 : (Ca + Mg)0 : H 2 is very 

 nearly 1:1:1:1, from which the formula H 2 ZnCaSi0 6 is de- 

 rived, in which the zinc and calcium are replaced to a slight 

 extent by manganese and magnesium respectively. The 

 formula may also be written (ZnOH) (CaOH) Si0 3 , and that 

 hydroxyl is present is proved by the fact that water is not 

 expelled much below a faint redness The formula is analo- 

 gous to that of calamine H 2 Zn 2 SiO B or (ZnOH) 2 Si0 3 . 



The pyrognostic properties are as follows : In the closed tube 

 at a gentle heat the mineral is unchanged, but at a temperature 

 approaching faint redness it exfoliates, whitens and gives off 

 water. Heated before the blowpipe the mineral exfoliates at 

 first, and then fuses at about 4 to a yellowish enamel. A 

 coating of zinc oxide is obtained when the mineral is heated 

 alone or with a little sodium carbonate on charcoal. The 

 powdered material dissolves readily in hydrochloric acid, and 

 gelatinous silica is obtained when the solution is evaporated. 



In conclusion we take great pleasure in expressing our sin- 

 cere thanks to Messrs. F. L. Nason and E. P. Hancock, who 

 have generously placed at our disposal all of the specimens of 

 this rare mineral which they have been able to collect. 



Mineralogical-Petrographical Laboratory, 



Sheffield Scientific School, March, 1898. 



