506 



RUM. MINERALS. 



still the nodule is compounded, containing a spherule 

 of calcareous spar within an investing crust of the mi- 

 neral. When long exposed to the air it decomposes 

 in the form of a rusty powder, which is thus occasionally 

 found filling those cavities that are visible on the surface 

 of the fragments in which it is found. The variety 

 from Fife differs from that of Rum in being less regular 

 in form, and less frequently round, while it is commonly 

 also of a larger size. From the most characteristic quality 

 of this mineral, the term chlorophseite may be conveniently 

 adopted to distinguish it.* 



* Since this work was prepared for the press the same mineral has been 

 brought from Iceland by Major Petersen. It is similar in all its charac- 

 ters to the specimens from Rum, but the nodule is of three or four times 

 the bulk. It is probable that, like other new substances, it will prove 

 less rare as the attention of mineralogists shall become directed to it. 



Considering our yet imperfect acquaintance with minerals, and the 

 uncertainty of the characters by which we are still compelled to distin- 

 guish them, it may possibly happen that the substance above described 

 may hereafter prove but a variety of some established mineral. At pre- 

 sent however its discriminating characters are strongly marked, while the 

 only chance of future investigation will be derived from giving it a con- 

 spicuous place in the list. Mineralogists will recollect how long many 

 substances of highly distinct characters were neglected, because over- 

 looked among the supposed varieties of some acknowledged species. 



