450 Mr. Levy on Murchisonite. 



specimens from Dawlish ; and instead of the silvery reflection 

 of light of the latter, presents a gold-yellow reflection, ge- 

 nerally not uniform but in spots. It somewhat resembles in 

 this respect the variety of felspar called sun-stone, and when 

 cut in a proper manner gives a similar play of light : but the 

 red max'l which is generally disseminated throughout the 

 crystal, prevents the effect from being so great as it may rea- 

 sonably be supposed it would have been had not that circum- 

 stance interfered. A further comparison between this sub- 

 stance and sun-stone would have been very interesting; but 

 I could not procure the sight of a rough sun-stone, to examine 

 whether it had any indication of cleavage ; and the very high 

 value set upon those which are cut, does not leave much hope 

 of our being allowed to cleave them. 



The natural plane itself parallel to the nacreous cleavage 

 presents frequently a gold-yellow reflection. Simple and ma- 

 cled crystals are also found divided in two parts by a thin 

 layer of red marl in a directicm parallel to the nacreous 

 cleavage, as if the crystal had been broken and cemented 

 again. Small perihexahedral crystals of black mica are 

 sometimes found in the interior of the crystals. Thin laminae 

 parallel to either of the two cleavages perpendicular to one 

 another, are sometimes transparent. The hardness of the sub- 

 stance is rather less than that of felspar. Mr. Kent has been 

 so good as to take with great care the specific gravity, and has 

 found it to be 2-5091 : I had found it somewhat lower, but I 

 give in preference his result, as being determined with greater 

 accuracy. Mr. R. Phillips has also had the kindness to ana- 

 lyse the substance, and has found the following result : 



Silica 68-6 



Alumina 16*6 



Potash 14-8 



100-0 

 I have now to state the reasons which induce me to consi- 

 der these crystals as belonging to a species distinct from fel- 

 spar. The characters which are common to both are very 

 apparent : they both possess cleavages in two directions per- 

 pendicular to each other; they have nearly the same hardness, 

 nearly the same sjiecific gravity ; and the analysis, although 

 indicating a greater proportion of silica and a smaller propor- 

 tion of alumina than the adularia analysed by Vaufjuelin, and 

 the common felspar analysed by Klaproth, — presents precisely 

 the same result as the analysis of glassy-felspar by the latter. 

 Finally, the macled crystals have a very remarkable resem- 

 blance to the macled crystals of felspar found in Auvergne 



and 



