350 Frof. Chapman on the Position ofLievrite 



prism-angle, 71° 10'); 1*684 (=V 4; prism-angle, 61° 47'). 

 In Lievrite, the two commonly occurring prisms give respect- 

 ively 0-6840 ( = V; prism-angle, 111° 12') and 1'370( = V2; 

 prism-angle, 72° 16'). To make these correspond with the chry- 

 solite values, the first prism must bear the symbol VJ, and the 

 second V 3. The vertical axes stand to each other very nearly 

 in the ratio of 5 to 4. But we need not attempt to push these 

 analogies beyond their legitimate limits. The affinity in general 

 characters and conditions of occurrence of Lievrite to Fayalite 

 (and through this latter to chrysolite) cannot be overlooked if we 

 take the entire relations of these substances into consideration. 

 Single characters, in the determination of analogies, are neces- 

 sarily useless. 



Now the atomic constitution of the chrysolites is perfectly well 

 established. The oxygen atoms in base and acid are equal, and 

 the base consists of simple oxides only, the general formula being 

 2(RO), SiO 2 ; or two atoms of monoxidized base + one atom of 

 silica. In the normal chrysolites the base consists of magnesia ; 

 in the olivines, of magnesia and protoxide of iron ; and in Faya- 

 lite (at least, essentially) of the latter oxide alone. In Lievrite, 

 on the other hand, as shown above, both protoxide and sesqui- 

 oxide of iron are present ; and the oxygen-atoms of the silica do 

 not correspond with those of the bases. 



In attempting to reconcile these discrepancies, I called to 

 recollection a fact that came under my notice some time ago. In 

 examining a specimen of Lievrite that had been broken up into 

 small pieces, I found, that certain fragments exerted a much 

 more powerful influence on the magnet than others. Whilst 

 some of the particles scarcely showed a trace of magnetism, 

 others were magnetic in a marked degree. These latter, tested 

 by the blowpipe, seemed almost free from silica; whilst the 

 feebly-magnetic fragments gave very readily, with microcosmic 

 salt, the well-known reaction of that substance. It occurred to 

 me, therefore, that the analysed specimens of Lievrite might 

 have contained a certain portion of magnetic iron ore, — a cir- 

 cumstance easily conceivable, if we call to mind the geolo- 

 gical associations of our mineral. The nearly uniform propor- 

 tions of the FeO and Fe 2 O 3 found in the various analyses seemed, 

 it is true, opposed to this idea ; but it appeared at least possible 

 that the crystallized specimens might be able to take up a certain 

 proportion, and no more, of the magnetic oxide. I calculated 

 therefore, from the first four analyses given above, the mean 

 composition of Lievrite, and reduced this, with the following 

 results, to 100 parts : — 



