José M. Soural : On <i Granile of Hemson (Sweden) 127 



Macroscopically it seems that there are crystals which can show 

 greatei sections than this, but that is probably because sometimes se- 

 vera! crystals cluster together in a vvay, that macroscopically it gives 

 the impression of a single individual. Below that máximum área occur 

 sections of extreme microscopical minuteness. 



The sections of greatest and least dimensions being connected by a 

 series of transitions. 



As muscovite, lepidolite and paragonite canfiot be distinguished 

 optically I used the micro-chemical method of Boricky for its final 

 determina tion and I fonnd that the mineral was the first namecl mica. 



Biotite. — The crystals are irregular and tabular according to (ooi). 

 Cleavage perfect, parallel to the basal pinacoid. The lamellae are 

 always bent. The dimensions of the crystals are about the same as 

 those of muscovite. Ng = Nm = green >■ Np = brownish yellow. 



Tiiis mica is uniaxial and the birefringence relatively low. It ap- 

 pears to be somewhat below o,o3. 



Ferrugineous inclusions are common. Pleochroic halos aroimd in- 

 clusions are common. The pleochroism being more pronounced in 

 the halos than in other parts of the crystal. 



Kiotiíe appears in less quantity than muscovite. Sometimes both 

 mica varieties occur together with parallel orientation. 



Apatite, — The crystals are generally irregular but sometimes they 

 show crystal faces. Their dimensions are variable. There are relatively 

 large crystals, the optical properties of which I have determined and 

 there are very small ones, acicular in shape, includecl in the other 

 minerals, the optical constants of which are impossible to ascertain, 

 and consequently their classification is not sure. In a section parallel 

 to the axis of one of the greater crystals I found that the dimensión 

 in th? direction of the axis was o, 38 mm. and perpendicularly p,45 

 fflin. consequently it was somewhat ílattened in the direction of the 

 axis, but generally the elongation is negative. The section was limited 

 by (0001) and (1010) and cleavages according to these faces were ob- 

 seivable. The best cleavage was that according to (oooi). The bire- 

 fringence Ng — Np =0,0027. The negative sign of the mineral was 

 also ascertained. 



Hematite and Magnetite. — These minerals occur as microscopical 

 inclusions in the feldspars and micas. It is the hematite which gives 

 the reddish colour to the feldspars oceurring as very small flakes 

 generally arranged parallel to cleavage planes. 



