Abstract of an Account of Crystallisations , fyc. 251 
The following varieties of this artificial magnetic iron-ore are 
enumerated bv Koch : 
%/ 
a. Foliated magnetic iron-ore . 
a. Common . Crystallised. 
b. Lamellar. In larger portions, disseminated in cornu 
pact magnetic iron-ore. 
b. Slaggy magnetic iron-ore. Imbedded in the compact, 
resembling that of Unkel on the Rhine, which occurs 
in basalt. 
c. Compact magnetic iron-ore. Massive. 
The following crystallisations were observed by M. Koch ; 
1. The fundamental form, is the regular octahedron, per*, 
feet. Sign O, Mohs. 
2. Octahedron, elongated in the direction of a prismatic 
axis. 
3. Octahedron, slightly truncated on all the angles. Sign 
H, O, Mohs. 
4. Cube slightly truncated on the angles and edges. Sign 
H, O, D, Mohs . 
The crystals 1, 2, and 3. have a splendent metallic lustre,—® 
the less perfect crystals a dull and rough surface, and the first 
sometimes exhibit a variegated tarnish. They are always 
grouped together in great numbers, and it is remarked that the 
crystals of the fundamental form are frequently grouped in rows. 
They seldom attain the size of a line, Crystals of this mineral 
are also formed where plates of iron highly heated, come in con- 
tact with a aqueous vapour ; and M. Mordenskiold informed Mr 
Koch, that artificial crystals of magnetic iron-ore are formed by 
the melting and gradual cooling of common magnetic iron-ore, 
II. Oxide of Zinc. Calamine. 
Hausmann, as mentioned in a former number of the Edin«> 
burgh Philosophical Journal, mentions this product as occurring 
in iron smelting furnaces: The following forms are described 
by M. Koch, which we enumerate according to the method of 
Mohs. The artificial oxide of zinc belongs to the prismatic 
system of Mohs. The fundamental form is described by Koch 
as an obtuse scalene four-sided pyramid, in which the ratio of 
