190 PHYSIOGRAPHY. CLASS II. 



lowest degrees upon Pr -|- oo, Sp. Gr. = 2-661 , 

 a crystal from Cornwall. 



Compound Varieties. Small reniform and glo- 

 bular shapes, and imbedded nodules ; also super- 

 ficial coatings of dusty particles. Composition im- 

 palpable, earthy or easily reduced to powder. 



OBSERVATIONS. 



1. The forms of the present species possess a remarkable 

 analogy with those of other hemi-prismatic species, par- 

 ticularly of prismatoidal Gypsum-haloide and prismatic 

 Cobalt-mica. 



The cornish varieties in transparent crystals have been 

 distinguished from the rest under the name of Vivianite. 

 The rest of the crystallised varieties under the denomina- 

 tion of the Prismatic Blue Iron, were again separated from 

 the compact and earthy varieties, or the Earthy Blue Iron. 

 These distinctions, however, seem to foave been introduced 

 only from the succession of the discovery in regard to the 

 varieties which they comprehend, and not from any scien- 

 tific or classificatory principle. 



2. In two varieties, a friable one analysed by KLAPROTH, 

 and a crystallised one from Bodenmais in Bavaria by Vo- 

 GEL, the following chemical constituents have been dis- 

 covered : 



Protoxide of Iron 47'50 41-00. 



Phosphoric Acid 32-00 26-40. 



Water 20-00 31-00. 



Its chemical formula, derived from the second analysis, is 



Fe 2 P + 12 Aq, which corresponds to 43*88 protoxide of 

 iron, 22-28 phosphoric acid, and 33-84 water. It decrepi- 

 tates before the blowpipe, but melts, if first reduced to 

 powder, into a dark brown or black scoria, which moves 

 the magnetic needle. It is soluble in dilute sulphuric and 

 ftitrie acids. The friable varieties are found white in their 



