Siberia?i Minerals. 27 



This form, from the relative po- p- ^ 



sitiou of its planes, and the angles 

 they measure, may be derived from ..^--^^^^^^^^X, 



an acute rhomboid, the planes of /W— — rX\ 



which would be the planes P of the e// ./--r > A 



figure, and measuring the same an- /h^ \ \ v ^ i V^ 

 gle, or very nearly the same angle, y-yl j i ^J ^^J 



as the primitive rhomboid of spe- XAKi f-^ 



cular iron. The faces e^, as shown \t\ ' J^ 



by the figure, are not repeated sym- ^-^ — l^ 



metrically on each side of the faces 



P ; so that there are only six of them, and they are disposed m 

 such a manner that each of the three planes e, of the upper 

 part of the crystal is paraUel to one of the planes e, of the lower 

 part This regular want of symmetry is precisely the charac- 

 ter ofiPered by the crystals of axotomous iron ore. It is what 

 Professor Mohs has expressed in saying that the regular forms 

 of this substance are hemi-rhombohedral with parallel faces. 



The crystals represented by fig. 1. are of a dark u-on black 

 colour ; their planes are sufficiently brilhant for the use of the 

 reflective goniometer, but however do not afl-ord very good 

 reflections! There are on some of them indices of cleavage m 

 a direction perpendicular to the axis. They act upon the mag- 

 netic needle, but not so powerfully as specular iron. Iheu- 

 size vary from more than an inch m diameter to about one- 

 fourth of an inch, their thickness is generally less than their 

 breadth. Sometimes are found adherent to them sma 1 cry- 

 stals or fragments of white felspar. Their exact locality, as 

 well as that of the other minerals above mentioned, is the 

 neighbourhood of Lac Ilmen, west of Miask, in the govern- 

 ment of Ecatherinebourg in Siberia. 



The specimen sent as Gadohnite presents a very large cry- 

 stal said to belong to that species, placed on flesh-coloured 

 cleavelandite, or perhaps rather labradorite, as one of the two 

 faces of cleavage, inclined to each other at an angle ot about 

 93° 30', is striated parallel to its intersection with the other; a 

 character which I believe belongs to the last-mentioned sub- 

 stance. The form of the crystal is that of an obtuse rhombic 

 prism, the acute lateral edges of which are emai-gmated by 

 narrow planes, widiout any distinct termination. 1 he laces 

 of the prism are rough, and small crystals of light brown zircon 

 are disseminated on them as well as in the matrix. 1 he crystal 

 is so engaged, that the incidence of the faces cannot be mea- 

 sured even with the common goniometer. The tracture is ot 

 a deep black with a resinous lustre. , j i r 



The zhcons have come in crystals, detached and also disse- 

 g 2 mmatea 



