CHURCH ON NEW AND RARE CORNISR MINERALS. 11.-Clm,&cal Researches on New and Rare Cornish Minerals. By Professor CHURCH,M.A. (Read November 18th 1869.) No. 6 Hisingerite. LAST summer I obtained from Mr. Talling of Lostwithiel some specimens of a dark brown amorphous mineral which he had recently found and which for some time appears to have been mistaken for beraunite. I have noted the occurrence of the same brown substance upon a specimen of tamarite &om Wheal Gorland in my possession. B2 CHURCH'S CREMICAL RESEARCHES Qualitative analysis showed the mineral to coiisist of ferric oxide silica and water with traces of magnesia and rarely of ferrous oxide. The chemical and physical characters of this Cornish mineral approach those of hisingerite or its varieties.Unwilling to increase unnecessarily the number of mineral species I shall provisionally describe it as hisingerite. The following are the chief characters of the supposed hisin- gerite :-Amorphous reniforrn fissured dark brown. Streak pale rust brown (in some specimens olive brown). Fragile ; fracture irregular conchoYda1. Hardness 2-75; density 1.74. Before blowpipe in closed tube much water having faint per- manent acid reaction. On charcoal decrepitates and becomes black. Fuses with difficulty in outer flame to a red brown bead. Boiled in acids leaves a silicious skeleton The Cornish hisingerite is very hygroscopic a specimen lost 28.65 per cent. in vacuo over sulphuric acid. But when the powdered mineral thus freed from accidental moisture was heated to loo' its further diminution in weight amounted to no more than 0.54 per cent.In the following analysis the sub- stance was therefore dried at 100' till constant :-Analysis. Substance FeaOj. Si02. H20. taken. I. -195 -07 -019 11. *136 *072 *0495 00155 111. ~1345 --01 4 Reduced into mean percentages these results stand thus :-Fe,O .......... 52.94 SiO .......... 36.14 H20 .......... 10.49 99.57 The mineral was found to contain 0.82 per cent. of P20 and traces of magnesia. In the above iron determination the P,O was excluded since the permangaiiate process was used to control the result of the direct precipitation of the ferric oxide. The oxygen ratio between the ferric oxide the silica and the water is 15 18 16 or 5 6 5 nearly.But the ratio 3 :4 :2 is not only simpler but probably represents the triie relation ON NEW AND RARE CORNISH MINERALS. of the constituents of the mineral more exactly. The corre-sponding formula is Fe20,.2Si02.2aq. The percentages de-manded by this expression together with those deduced from the before-mentioned ratio and from the experiments are here compared :-Theory. 1 c- -. I. 11. Experiment. Fed03.2Si02. 2H20. 5Pe2O,.9SiO2.8HdO. Fe,O,. ......... 50-63 53.74 52.94 si0 .......... 37.98 36-58 36.14 H,O ......... 11.39 9.68 10.49 100~00 100*00 99.57 The chief discrepancy between Theory No. I and experiment lies in the percentages of ferric oxide which is 2.31 per cent.higher thanit should be This arises partly from the presence in the specimen analysed of traces of ferrous oxide and partly from the difficulty of separating the hsmatitic matrix from the portion of the mineral taken for examination. Thus not only has the iron percentage been raised but the silica and water percentages have been reduced below those required by the forrrda Fe20,.2Si0,.2H,0. Owing chiefly to the imperfect methods of drying minerals for analysis the analyses of hisingerite previously made are not easily interpreted into a definite formula the percentage of water found by different chemists varying between 11.54 and 22.83. If the Cornish mineral now under discussion be rightly assigned to hisingerite its analysis may throw some light on the constitution of that species and at any rate introduces a mineral new to Britain.It is instructive to note in this con- nection that if we correct the percentages of water found iiz the analyses of liisingerite from various localities by deducting where known the proportion lost at looo the mean percentage result approaches very closely to that obtained in the analysis of the Cornish specimens. But it should be stated on the other side of the question that the density of the Cornish mineral in its natural condition is only 1.74 while that of hisingerite is about 2.5 and that there are also further differences both chemical and physical but generally minute between the English and foreign specimens of the mineral.