RE-EXAMINATION OF AMERICAN MINERALS. 133 



Ca 6 Si 2 4-B 3 Si 2 +3H=Datholite. 

 Ca 3 Si 2 +B 3 Si 2 =Danourite. 



This mineral forms then the second natural borosilicate of lime. 

 Its physical characters have been fully described elsewhere. 



The results of the analysis somewhat surprised us, as we 

 confidently expected to find alkalies; of course much care was 

 directed to the settling of this question, which from the sim- 

 plicity of the composition of danburite was easily done in 

 the following manner: to one gramme of the mineral strong 

 hydrofluoric acid was twice added, the mass carefully heated 

 and evaporated nearly to dryness on each addition ; finally 

 sulphuric acid was added in excess, the whole evaporated to 

 dryness and ignited; the residue weighed 563 milligrammes, 

 of which 544 were sulphate of lime, the remaining 19 being 

 composed of alumina, iron, manganese, and magnesia. The 

 544 milligrammes of sulphate of lime, correspond to 22.44 per 

 cent, of lime in the mineral used, proving clearly that the 

 remainder was all volatilized under the action of hydrofluoric 

 acid; which, according to previous experiments, was shown to 

 consist of silicic and boracic acids. Three repetitions of the 

 above experiment gave perfectly concordant results: in fact no 

 more beautiful proof could have been had of the absence of all 

 other bases but lime in any very sensible quantity. Moreover, 

 the amount of lime thus indicated agrees perfectly with that 

 obtained by the direct method of analysis. 



The boracic acid was estimated by first ascertaining the 

 exact amount of silica by a soda fusion, and then deducting 

 this quantity from the entire loss of a given quantity of the 

 mineral under the action of hydrofluoric acid. 



The specimens examined were among the finest that have 

 ever been found, and were procured by Mr. Brush at the 

 locality. 



28. Carrollite, a Copper Linn^ite. 



This mineral occurs at Finksburg, Carroll County, Maryland, 

 and was described as a new species by Mr. W. L. Faber.* He 

 gave as its chemical composition 



s Co -m Cu 



27.04 28.50 1.50 32.99 

 Formula 2Co S- 



*Amer. Jour. Science and Arts, 2d series, vol. xiii, 418. 

 10 



Fe 

 5.31 



As 

 1.82 



Si 

 2.14 



Cu 2 S. 







