May 23, 1 872 J 



NATURE 



71 



-pi 



ON THE MINERAL CONSTITUENTS OF THE 

 BREITENBACH METEORITE f' 



'HE Siderolite of Breitenbach was acquired for the British 

 Museum in the year 1863. It was found (in 1861) at 

 Breiteniiach in Bohemia, at a spot not very far distant from the 

 Saxon frontier, or indeed from Rittersgiin, in Saxony, a place 

 in which a very fine mass tliat Ijears a close resemblance to the 

 Siderolite of Breiienbach, was almost contemporaneously found. 

 A little way to the west of the centre of the line joining Ritterc- 

 griin and Breitenbach lies S'cinbach, a village in the environs of 

 Johanngeorgenstadt, near Schwartzenberg ; and here in 1751 

 was also found a mixed meteoric mass in which, as in the two 

 already mentioned, iron, sponge-like in its structure, encloses 

 siliceous minerals that do not present a familiar aspect. The 

 three meteorites are, in fact, so similar to one another and sj 

 dissimilar to any others in European collections, that there can 

 be little doubt they belonged originally to the same meteoric 

 fall. 



Stromeyer t in the year 1S25 examined a siderolite in which he 

 found as much as 61 'S per cent, of silica. This remarkable 

 result, together with the numbers of his analysis, he interpreted 

 as indicating the presence of a magnesian tribilicate, probably 

 meaning thereby a sesquisilicate (magnesium epideutosilicate). 

 The specimen which he analysed he described as coming from 

 Gtimma, in Saxony. This specimen was, in fact, a portion of a 

 mass preserved in the collection of the Duke of Gotha, and 

 doubtless believed by Stromeyer to be a portion of a stone which 

 was known to have fallen in the middle of the sixteenth century 

 in a wood near Naunhof, in the neighbourhood of Grimma. 

 Chladnif, however, held this view to be untenable, grounding 

 his opinion on the completeness of the meteorite preserved at 

 Gojha, both as regards its form and its crust, while he adds that 

 the Xaunhof ma^s must have been far too great to allow of its 

 being transported, and, indeed, that it had never been redis- 

 covered. It is in every way probable that the material Stromeyer 

 really had taken to work upon \\'as from a Saxon locality, and in 

 fact a spf cimen from a fall, to which the Rittersgriin and Breiten- 

 bachasiderolitesbelorg. Breithaupig believes the fall in question 

 to have been the " Eiseiiirgen" which occurred at Whitsuntide, 

 1 164, in Saxony, when a mass of iron fell in the town of 

 Meissen II . 



An inspection of a polished surface of either of these masses 

 reveals the iron in patches of irregular form, which exhibit the 

 characteristic crystalline structure of meteoric irons when etched. 

 The interspaces are partly filled by meteoric pyiites (troilite) in 

 small patches, recognisable by its pinchbeck brown colour, the 

 rest of the surface being occupied by a greenish and greyish- 

 brown crystalline magma. It is of the ingredients of the last- 

 mentioned portion of the meteorite that I sIi.tU first speak On 

 treating the whole mass with mercuric chloride at 100° fur some 

 hours the iron and the troilite arc dissolved, and the magma 

 before alluded to remains unattacked. But it has now lost its 

 compound structure, and is found to consist of three substances : 

 (l) highly crystalline, bright green, or else greenish-yellow 

 grains ; (2) rusty brown, sometimes nearly black, sometimes also 

 nearly colourless grains of a mineral that presents crystalline 

 features, but on which definite crystalline planes are ot great 

 rarity ; and (3) crystalline grains of chromite. 



Tire first of these three minerals pioved to be a ferriferous 

 enstatite, or brorzile ; the .second is a mineral which corresponds 

 in all respects, except its crystalline form, with the tridymite of 

 Prof. Vom Rath. In respect of their forms, however, it is diffi- 

 cult to suppose that the two minerals are identical. 

 Broiizitc ofthcBrciieubacli Siderolite 



The specific gravity of this mineral is 3 '238, that of the sili- 

 cates in the Steinbach siderolite,' as determined by Stromeyer, 

 having been },2'l(>, and as estimated by Rumler 3 '23.. The hard- 

 ness is 6. 



The blackened aspect of some of the bronzite was due to a 

 mere superficial coating of iron oxide, arising doubtless from the 

 oxidation of a portion of the nickeli'erous iron. It was in- 

 variably found that this film was easily removed by hydrogen 

 cliloride, leaving the bnnzite of a bright green colour, and that 

 the action of the acid on the mineral extended no further. 



* Abridged from a paper contributed to the Phllcsophical Transactions 

 by Prof. M.tskelyne, F.k.S. 

 t Pogi!. Aun iv. p. 195 

 t Berg. jnd. Hutt, Zeitung, xxl. p. 323 

 § Feuer-Meteore,|pp. 326 and 313 

 II Fcuer-Met«ore, p. 198 



Two analyses of this mineral were made, the one by the 



hydrogen fluoride method of distillation*, the other by fusion 



with mi.\ed alkaline carbonates, and the results were as 

 follow : — • 



I. 11. Mean. Oxygen. 



Silicic acid . . . 56-101 5(3002 56051 2989 



Magnesium oxide . 30'2I5 31 '479 30 S47 I2'34 



Iron protoxide . . 13-583 13-295 13-439 297 



99-S99 100-776 100-337 

 These numbers correspond very closely w-ith the formula 

 (Mgf Fe-^) Si O3. 



Asinaiiite — a new mineral, being Silica crystallised in the Rhombic 

 System, as a Constituent of the Breitenbach Sidtrolite. 



The second mineral associated with the bronzite in this 

 meteorite is free silica, possessing the lighter specific gravity 

 presented by quartz after fusion, and crystallised in forms that 

 belong to the orthorhombic system. To this mineral, which is 

 distinct in its systenr and forms from the tridymite of Vom Rath, 

 I propose to give the name Asmaniie, A'sman Keing the Sanscrit 

 term (corresponding to the Greek ukjioij/) for the thunderbolt of 

 Indra. In bulk it forms about one-third of the mass of mixed 

 siliceous minerals. The grains of this mineral are found mixed 

 with those of the bionzite, after the iron, the troilite, and the 

 chn mite have been removed. They are very minute and much 

 rounded, and, though entirely crystalline, they very rarely indeed 

 present faces that offer any chance for a result with the gonio- 

 meter ; indeed out of the several thousands of these little grains 

 comprised in some two grammes that were isolated of the 

 mineral, it was only possible to find with a lens about a dozen 

 specimens with sufficiently distinct crystallographic features ; 

 and of these only four or five proved to bs available for examina- 

 tion and comparison. In several, however, the optic axes were 

 plainly to be distinguished when properly examined with a 

 NiJrrenberg's polarising microscope ; and by this means the 

 angles given by planes belonging to zones otherwise too incom- 

 plete for a reliable result were brought into comparison on 

 different crystals. 



The parametral ratios of Asmanite are 



a:b:c^- 1-7437 : i-oooo : 3-3120. 



The taces of the octaid forms are almost invariably rounded. 

 Fair approximate measurements, however, of three of the tanto- 

 zonal faces in one crystal were obtained. 



That the mineral belongs to the rhombic and not to an unaxial 

 system is emphatically evidenced, independently of the measure- 

 ments, by i's optical characters, as shown in its very distinct and 

 widely separated optic axes. As has been said, the first mean 

 line IS the normal of the face i o o, that to face o o i is the 

 second mean line. The first mean line is parallel to the axis of 

 least optical elasticity, to that the crystal is positive in its optical 

 character. The apparent angle,- as measured in air, of the optic 

 axes was approximately determined as 107° to 107° 30'. The 

 ;.xes for the red rays are slightly more dispersed than those for 

 the blue. 



The crystalline grains which constitute this ingredient of the 

 meteorite, when first obtained, are of a rusty brown and some- 

 times even black colour ; treatment for a short time with dilute 

 hydrogen ch'oride, however, entirely removes this iron stain and 

 leaves the granules in a state of colourless purity, in which 

 state they are readily distinguished from the grains of the accom- 

 panying bronzite. 



The specific gravity of the mineral gave the number 2-245. 

 Its hardness is 5-5. 



Two analyses were made by different methods, and the results 

 are given below. 



I. 0-3114 substance, distilled with pure hydrogen fluoride, 

 gave I -1 136 gramme of potassium fluosilicate, o C035 gvamire 

 iron oxide, oooiS calcium oxide, and 0-0132 gramme magnesirra 

 phosphate. 



These determinations denote the following percentages : — 



Silicic acid 97'43 



Iron oxide 1 -124 



Calcium oxide o'578 



Magnesium oxide I'Sog 



100-641 

 * Philosophical Transactions, 1870, p. 189, 



