Dana and Penfield — Mineralogical Notes. 139 



The quantity of these tabular crystals was too small to admit 

 of its being proved that they have the same composition as the 

 hexagonal prisms, but everything points to that conclusion. 



The substance was readily soluble in even very dilate, cold 

 nitric acid: the solution upon evaporation yielded gelatinous 

 silica. Before the blowpipe readily fusible. Specific gravity 

 of crystals 5 '92. For analysis the compound was dissolved 

 in cold, dilute nitric acid and the insoluble magnetite filtered 

 off. Two analyses were made (Penfield); for the first (I) 

 only distinct crystals were taken, of which '7073 grams were 

 selected ; the result after deducting 0-44 per cent of magnetite 

 is given below. The second analysis (II) was of the crystalline 

 part of the slag. The result is given after deducting *207 per 

 cent of magnetite. The presence of a trace of carbonic acid, and 

 a very minute trace of phosphoric; acid was distinctly proved. 



I. Crystals. Ratio. II. 



Si0 8 



17-17 



•286 



PbO 



7-2-39 



•325 



FeO 



0-51 



•007 



CaO 



7'48 



•134 



MgO 



0-56 



•014 



Na 2 



0-35 



•006 



•486 



98-46 



Massive 



portion. 



Ratio. 



SiO a 



16-00 



•267 



PbO 



75-26 



•338 " 



FeO 



0-74 



•010 



MnO 



17 



•002 



CaO 



6-15 



•110 j 



M14O 



0-50 



•012 j 



Na 3 



0-24 



•004 



C0 2 



trace 





•476 



99-06 



The ratio in I for SiO a :RO = -286: 486=1: 1*70=4: 7 nearly. 

 For II the ratio is Si0 2 : R0=267: 476 = 1: 1-78 = 4: 7 nearly. 

 The agreement between these shows that the formula, R 7 Si 4 15 , 

 must express very closely at least the true composition of this 

 artificial lead silicate. The occurrence of so rare a compound 

 is especially interesting in connection with the recent discovery 

 of native lead silicates, notably at Langban, Sweden. 



These natural lead silicates include the three following from 

 Langban: ganomalite, a silicate of lead and manganese with 

 small quantities of lime and magnesia ; hyalotekite, a silicate 

 of lead, barium and calcium ; melanotekite, a silicate of lead 

 and iron. To these should be added kentrolite, from southern 

 Chili, a silicate of lead and manganese. All of the minerals 

 named are crystalline in structure, but kentrolite alone has 

 been found in distinct crystals. We do not know that any 

 artificial crystallized lead silicate has been described hitherto. 



