456 Oxide of Chrome. 



NATIVE OXIDE OF CHROME *. 



The combinations of this metal with two others, namely lead 

 and iron, under different forms, have for some time found a place 

 in our catalogues of minerals. A place must now also be made 

 for chrome itself in that division of mineralogical systems which 

 is allotted to the metals. I am not aware at least, that the oxide 

 of chrome has yet been found by any one in a native state ; cer- 

 tainly it has not been enumerated in any system of mineralogy. 



I have recently discovered it here in Shetland, in the island of 

 Unst. It is found in cavities in the chromate of iron, which 

 abounds in this island, so as, for the space of many miles, to be 

 scattered over the surface of the ground, and even to be used in 

 common with the loose stones which it accompanies in the building 

 of dykes. 



This oxide is easily recognised by its beautiful green colour, 

 and does not seem to differ from the green oxide produced in our 

 laboratories bv the action of heat. In some places it is merely 

 diffused through the fissures of the ore; in others it occupies 

 cavities resembling those of the amygdaloids. It is sometimes 

 found in a powdery form ; but at others it is compacted into a 

 solid substance, bearing the marks of a crystalline structure, and 

 somewhat translucent. Altliough it appears to be in abundance, 

 when the specimens that contain it are broken, that effect is only 

 the consequence of the brilliancy and contrast of its colour with 

 the black and dark gray of the surrounding chromate of iron. It 

 would be very difficult to collect many grains of it in a separate 

 state from any of the fragments of the black ore which I ex- 

 amined. 



The green oxide is accompanied by a yellow oxide of chrome, 

 in cavities generally distinct from it, but sometimes intermixed, 

 and in somewhat less abundance. This latter is more generally 

 in the form of powder than the green. As the green oxide of 

 chrome changes to yellow by heating it, M. Vauqueiin appears to 

 think that these are distinct oxides ; but this point does not seem 

 to have as yet been very satisfactorily examined. For the present 

 purposes it will, at any rate, lie more convenient to consider them 

 merely as varieties of one mineral species. Those mineralogical 

 writers who are desirous of increasing the number of species may 

 easily follow a different course. 



The mineral distinction of the oxide of chrome may be com- 

 prised in the following terms: 



Oxide of Chrome. — This mineral is of a bright grass green co- 

 lour, or else pale yellow ; and is found either in a powdery or a 

 compact form. In the former case, the aspect is dull; in the 



* Journal of Science, No. 21 . 



latter, 



