386 



DESCRIPTIVE MINERALOGY. 



Geological Situation. Specular iron ore occurs in beds or veins in the primary or lower 

 transition rocks. It has not been found in extensive deposits in the secondary ones. 



LOCALITIES. 



As in the preceding species, I must refer the reader for a full account of the New- York 

 localities of the specular iron ore, to the first part of this work (p. 23). I here add only a 

 few notices of a purely mineralogical character. 



In the county of St. Lawrence, this mine- 



Fig. 446. 



Fig. 447. 



ral is often found in the form of crystalline 

 plates, the edges of which are rounded as in 

 Fig. 446, being modifications of very obtuse 

 rhombohedra. Fig. 447, and quite similar to 

 the lenticular crystals of calcareous spar 

 (see Fig. 70). Sometimes these crystals are 

 nearly flat, and have a hexagonal outline. 

 Perfect forms are very rare. The semi- 

 crystallized varieties are usually associated with the dodecahedral crystals of quartz. 



LIMONITE. 



limonite. Beudant and Shepard. — Hydrous Peroxide of Iron. Thomson. — Brown Oxide of Iron, and Argil- 

 laceous Oxide of Iron. Cleaveland. — Prismatic Iron Ore. Jameson. — Hydrous Oxide of Iron, Eind Brown 

 Hematite. Phillips. — Brown Iron Ore. Dana. — Prismatisches Habronem-Erz, and Prismatoidisches 

 Eabronem-Erz. Mohs.* 



Description. Colour various shades of brown, sometimes yellowish. Streak yellowish 

 brown. Without action on the magnet. It very rarely occurs crystallized, but it usually 

 presents stalactitic, botryoidal or mammillary forms having a fibrous structure ; it is also mas- 

 sive and earthy. The primary form said to be a right rectangular prism, {Phillips) ; a right 

 rhombic prism, {Mohs) ; a cube ? {Beudant). Fracture uneven, even, conchoidal, or earthy. 

 Lustre more or less adamantine. Opaque or translucent on the edges ; crystals said to be 

 sometimes semi-transparent, and showing a blood-red colour. Hardness from 5.0 to 5.5. 

 Specific gravity from 3 . 37 to 3 . 94. Infusible by the blowpipe, but gives out water by cal- 

 cination, and most of the varieties become black or reddish black and magnetic ; with borax, it 

 melts into a green or yellow glass. Soluble in heated nitro-muriatic acid. 



Composition. Peroxide of iron 82.00 to 84.00, water 11.00 to 14.00, oxide of manga- 

 nese 2.00, silica 1.00 to 2.00. It is therefore a hydrous peroxide of iron, and contains, 

 when pure, peroxide of iron 85.30, and water 14.70. Formula FcaOs+Aq. 



* In the first part (page 29), lAmonite is incorrectly referred to the Rhombohedral Iran Ore of Jameson and Mohs. 



