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can perceive that in these places the mineral is traversed by a 

 number of cracks running in a vertical direction, and often that 

 in these cracks a dark opaque substance has been deposited, 

 which probably is iron in some state of oxidation. The altera- 

 tion, therefore, probably consists, in part at least, in the separa- 

 tion of iron from the mineral substance. By this separation 

 the mineral loses its dark colour, the pleochroism likewise 

 decreases and vanishes, and light-coloured zones and spots, 

 microscopically visible, arise on the faces of the crystals. The 

 microscopical cracks gradually become wider and more numerous. 

 At last the columns remaining between the cracks are resolved 

 into an aggregate of extremely diminutive crystals, often deve- 

 loped on all sides. These adhere so loosely to one another that 

 they can be separated for instance by the touch of a soft brush. 

 In colour they are yellowish brown with a tinge of green. They 

 are elongated, of monoclinic habit, tabular parallel to the second 

 pinacoid, and terminated by an oblique face, which makes an 

 angle of about 40° with the first pinacoid. They have very 

 strong double refraction so that, in spite of their thinness, they 

 show between crossed niçois a most vivid play of interference 

 colours. Under the microscope they are wine-yellow in colour 

 and without any perceptible pleochroism. One extinction-direc- 

 tion makes an angle of about 7° with the longitudinal direction 

 and towards the same side on which the oblique terminal face is. 

 This extinction-direction coincides with the direction of the 

 greatest velocity of light. The characters now enumerated justify 

 the opinion that the mineral described is a new variety of 

 aegirine , poor in iron and being the result of an alteration of 

 common aegirine. The characteristics of this variety would be 

 its light colour and strong double refraction. The oblique ter- 

 mination corresponds to the pinacoid of the second order {lOl}. 

 At the locality No. 9 the aegirine has been subject to 

 strongly acting decomposing processes. The decomposition 

 has taken place both on the ends of the crystals and on their 



