SCACCHI HUMITE : DAUBREK BAS-RHIN. 11 



On the HuMiTE 0/ Monte Somma. By M. A. Scacchi. 



[Poggend. Annal. supplem. vol. iii. p. 161 et seq. Leonhard u. Bronn's N. Jahrb. 

 fiir Min. u. s. w. 1853, p. 76.] 



HuMiTE belongs to the rectangular prismatic system*. The crystals 

 are remarkable for exhibiting three typical forms ; each of these 

 being distinguished by definite faces, almost all of which are dif- 

 ferent from those of the other types. This fact is of the more im- 

 portance, inasmuch as the sometimes very numerous faces of the 

 crystals belonging to one and the same typical form can be derived 

 by very simple laws from the proportional length of the axes of the 

 primary form. This is not, however, the case with the faces of the 

 crystals of different types, which can only be derived from the same 

 primary form by more or less complicated laws. (The author's in- 

 teresting crystallographic details illustrative of this subject, could 

 not be understood without the aid of very many figures.) 



The Humite crystals are only found among the loose blocks of 

 Monte Somma, in granular limestone, and in a peculiar rock, of gra- 

 nitic structure, consisting of whitish olivine, mica, and magnetic iron. 

 In the limestone the crystals of humite occur on the surface of geodes, 

 or slightly covered by the limestone, and nearly always accompanied 

 by zeilanite and crystals of green mica. In the latter rock, it is 

 mostly associated with zeilanite, idocrase, garnet, and small yellow 

 crystals of augite. More rarely humite is met with in many other 

 rocks, in company with the above-named substances. Its colour is 

 very variable, mostly brown, reddish-brown, yellow or white. Spe- 

 cific gravity, 3*2 ; hardness, that of felspar. Before the blow-pipe it 

 is unchanged. The pulverized mineral is easily decomposed by heated 

 hydrochloric acid. 



The author also remarks, in comparing the crystals of humite with 

 those of olivine, to which they have much similarity in their geo- 

 metrical properties, that an agreem.ent in the chemical composition 

 of the two minerals may readily be conjectured. [T. R. J.] 



Description Geologique et Mineralogique du Bepartement du Bas- 

 Rhin. Par M. A. Daubree, Iirg. des Mines, &c. pp. 500. 8°, 

 Strasbourg, 1852. "With five coloured Lithograph Plates of 

 Sections, &c., and a large coloured Lith. Map. 



The Geological Map issued with this work is on a scale oi -^-^]j^y^, 

 and is a reduction from the larger mapf on a scale of yjyjjjj^, which 

 was prepared by M. Daubree, in 1840-48, by direction of the Council 

 General of the Department, and at the instance of the Director- 

 General of Bridges, Roads, and I\lines, who in 1835 recommended 



[* In Brooke and Miller's Mineralogy, 18r)2, Humite is described as " oblique," 

 and reasons are offered for this view of the crystallographic nature of the mineral 

 in question. — Transl.] 



t This is published in six sheets, printed in colours. The smaller map may be 

 also had separate. 



