Notices of Memoirs — Brief Abstracts* 367 



difficulty, and the mineral being therefore very tough. In conse- 

 quence of this fibrous texture, it is not easy to determine the precise 

 degree of hardness, but it is probably about five. Dr. Tschermak 

 describes two varieties of Ludwigite ; the colour of the one being 

 blackish-green, whilst that of the other is almost black, with a 

 slight tint of violet. Both varieties have been analyzed under Prof. 

 Ludwig, of Vienna, after wliom the species is named. 



No. I. is the green variety, with specific gravity 3-951 ; No. II. is 

 the black variety, with spec. grav. 4-016. 



I. II. 



Eoric anhydride 16-09 15-06 



Ferric oxide 39-92 39-29 



Ferrous oxide 12-46 , 17-67 



Magnesia 31-69 26-91 



100-16 98-93 



The second analysis leads to the formula : 3 MgO-B-O^+Fe O'Fe^O^ 

 The first analysis shows part of the ferrous oxide isomorphously re- 

 placed by magnesia. It appears, therefore, that Ludwigite is a 

 molecular combination of borate of magnesia with proto-peroxide of 

 iron ; the latter compound does not exist mechanically disseminated 

 through the mineral in the form of magnetic iron-ore, but appears to 

 be chemically combined with the borate. F. W. E. 



2. — RivoTiTE ; A NEW MiNERAL Species. Notc sur une nouvellQ 

 espece minerale de la Province de Lerida. Par M. X. Ducloux. 

 Comptes Bendus, 1874, Ixx^dii. No. 21, pp. 1471-1473. 

 Under the name of Bivotite — a name proposed in memory of the 

 late M. Eivot, of the Ecole des Mines — a new Spanish mineral 

 is described by M. Ducloux. It occurs in small irregular masses 

 disseminated through a limestone, on the western slope of the Sierra 

 del Cadi, in the province of Lerida. Rivotite is a compact amor- 

 phous substance, varying in colour from yellowish green to dark 

 greyish green. Its hardness is between 3-5 and 4, whilst its specific 

 gravity varies from 3-55 to 3"62. According to M. Ducloux, the 

 composition of Eivotite may be expressed by the following formula : 

 Sb^O^-f 4(Gu,Ag)O.Co2. P. W. E. 



3. — On Datoltte. Ueber Datolith. Von Edward S. Dana. 

 Mineralogische MittJieilungen, 1874, Heft i. pp. 1-6. 

 Two years ago Mr. Dana published in Silliman's Journal a paper 

 on the crystallographic characters of the well-known crystals of 

 Datolite from Bergen Hill. He has since extended his study of this 

 species, and has examined a fine series of specimens in Vienna. The 

 results of this work are given in the present paper, which relates 

 chiefly to the Datolite of Arendal in Norway, Andreasberg in the 

 Hartz, and Toggiana in Modena. The occurrence, the symbols, and 

 the angles of all the known faces are exhibited in a well-arranged 

 table ; whilst several figures of crystals are given in a lithographic 

 plate accompanying the paper. F. W. E. 



