SiJero Calcite. icg in a great meafure acceflary, as I cHd not mention that Mr. Woulfe himfelf fufpedted that vvhat he called magnefia was not true magnefia, bot a new earth. A ftone, however, of the fame na- ture as that which I had wrongfully afcribed to vvhat I called compound fpar, Baron Born afferts, has been found in the valley of Zillerthal in Tyrol, in a fteatitic rock.; the defcription he gives of it exadfly correfponds with that of Mr. Woulfe, except that it neither eff er ve fees nor dif- folves in acids, both which Mr. Woulfe expreflly fays the ftone defcribed by him does : the Baron therefore, in all probability was deceived. * i. From what has been la'id, itmay beinferred that braun fpar, or fidero-calcite, exhibits in its compoikion various gradations to or from the the fparry iron ore; like this it fometimes effer- vefces with acids, and fometimes t,his effervef« cence is fcarcely perceptible. Bayen. Mem. Etrang. 9, 704. 2 Berg/n. 198. 2. The proportion of calcareous earth varies confiderably in this ore, fo that fometimes it contains no more than 2 or ^ per ct.; and hence it efcaped the adtion of tartar vitriolate in Mr. Woulfe’s experiment; for, if felenite were formed, yet a few grains of it would remain diffolved, and affbrd no precipitate. 3. This ore contains manganefe, and it is this ’ which, with the vitriolic acid, formed white bit ter rhomboidal cryftals in Mr. Woulfe’s experi- ment; to this the fatifcence, or efflorefcence, or decompofition, of the fidero-calcite is owing. 4^ The varying denfity of this ftone is alfo an evident confequence of its varying compolition as well as texture. 8th Species.