101 PAPERS READ BEFORE THE CHEMICAL SOCIETY. III.-,Mineralogical Notices. By Prof. STORY-MASKELYNE and Dr. FLIGHT. 14. Cnledonite. SOME little time back a minei*al termed by the dealer who sold it to the British Museum aztrichalcite was bought by the Mineral Depart- ment. It was from Leadhills and though at first sight not unlike the mineral under the name of which it went it really bore much greater resemblance to some of the more fibrous and compact varieties of cale-donite. In the first place therefore it was analysed. The percentage composition of the mineral is given in Colurnn I in a subsequent part of this Notice. It will suffice here to say that that analysis led to a rationai formula represented by five equivalents of lead sulphate two of lead hydrate with three of cupric hydrate a composition in which a small amount of lend carbonate present in the substance is not included.A composition thus differing from that received for caledonite led in the next place to an investigation of the crystallographic elements of the mineral in question. The crystals however were microscopic and it was with some diEculty that two of them were found capable of being measured with any degree of accuracy ; one of these however when examined under the microscope in light polarised in a definite plane showed principal sections parallel to the edges of the prism in two planes which were afterwards proved to be perpendicular to each other. The measurements of the edges in the zone contaking these two faces gave angles approximately corresponding with those of the zone [100,001] of caledonite ; a zone perpendicular to this that namely of [100,010] was also measured and the angles in the two cases were :- As found.As in Caledonite. 100,101 . . * . 35" 16' to 3.5" 30' 35" 37' 101,001.. . . 54" 44'to 54' 30' 54O 23' l00,OOk * . . . 90" 90" 100,110.. . . 48" (approx.) 47" 15' 100,101.. . . 90" (approx.) 90" The crystals were too minute to afford measurements of any of the VOL. XYVII. I STORY-XASKELPNE AND FLIGHT’S angles in other zones or any more accurate determination of these ; indeed only one face that namely of 100 reflected a perceptible image into the telescope. The optical characters however prove the crystal to belong to an ortho-symmetrical system while the observed angles were sufficiently near to those established for caledoiiite to justify khe belief that the two minerals were crystallographically identical or nearly so.It was deemed desirable however that an analysis of undoubted caledonite should be made in order to see whether the received formula for that mineral was correct. The result has confirmed the goniometrical determinations by establishing for caledonite the composition above given for the mineral. In the analysis of the so-called aurichalcite it was found that the amount of lead sulphate lead oxide reckoned as carbonate and copper oxide already gave a total of one hundred although the water which the mineral contains had not yet been estimated.A determination of the actual amount of carbonic acid present mas then made and instead of 9.5 per cent. of that constituent as given in Brooke’s analysis only about 1.5 per cent. was found. The analysis of undoubted caledonite is given under I1in the follow- ing table:- I. TI. Mean. Lead sulphate ........ 60.23 59.49 59-86 Lead oxide .......... 25-12 26.19 25.66 Copper oxide ........ 9.41 9.178 9.294 Carbonic acid ........ 1.434 -1.434 Water .............. -3.701 3.701 99.949 As the mineral occurs in association with cerussite the carbonic acid is most probably present in the form of carbonate of lead. If then we eliminate this carbonic acid together with the corresponding amount of lead oxide the remaining constituents give the following equivalent ratios :-Lead sulphate ........0.395 .... 5 Lead oxide ........... 0.16 .... 2 Copper oxide ........ 0.23 .... 3 Water ............... 0.411 .... 5 which ratios accord with the formula 5PbS04 +. 3CuH20 + 2PbR2OZ indicating a composition corresponding with three equivalents of lina-rite two of lanarkite and two of water. It is not easy to ascertain how Brooke arrived at his results. In his MINERALOGICAL NOTICES. paper (Edin.Phil. JOUT., iii 117) he states that (‘the cupreous sulphato- carbonate appears . . . to consist of six atoms of sulphate of lead four atoms of carbonate of lead and three atoms of carbonate of copper if the carbonate of copper be chemically combined and not accidental.” No percentage numbers are to be found in his paper and those given by Dana (Sgstem of Mheralogy 5th ed, 626) are clearly not the re- sults of an analysis as the reader might suppose but are calculated numbers based on Brooke’s formula.15. Lanarkite. Pisani (Conzpt. rend. lxxvi 114) and Jannettaz (ibid. lxxvi 1420) and still more recently Schrauf (Mineralog. Mitt. 1873 heft 2 137) have shown that lanarkite is not a lead sulphate and car- bonate as Brooke and Thornson have stated it to be but a combi- nation of one equivalent of the sulphate with one of the oxide It seemed not improbable that the second equivalent of lead oxide might be in the form of hydrate. As this water would only constitute some- what more than 3 per cent. of the mineral and as Pisani’s analysis showed a deficiency of more than 2 per cent.it was considered advisable to analyse lanarkite with a special view to decide this point. A very pure specimen lost at loo” in one hour 0.008 per cent. ; in another hour at the same temperature the same trifling amount. When heated to just visible redness it gave off 0.149 per cent. of water and when it was exposed to a bright red heat for half an hour nothing further passed into the chloride of calcium tube. An analysis of the heated mineral gave the following numbers (PbSOI + PbO). Theory. Lead sulphate ,.... . 57.70 57.605 Lead oxide .....,.. 42.89 42.395 100.59 100~000 Lanarkite then contains no water and like caledonite no carbonic acid. It is of interest in connection with this subject to note that the maxite of Iglesias Sardinia examined last year by Laspeyres (Jour. Prakt. Chem. 1872 470) consists of lead sulphate in combination with lead carbonate and hydrate. I2