io6 REPORTS OF inve;stigations and proji-cts. 



lastonite. The /S-form of magnesium silicate is the magnesian pyroxene oc- 

 curring in meteorites to which no mineralogical name has yet been given. At 

 about 1,365° it is transformed into an orthorhombic form quite distinct from 

 enstatite and unknown in nature. 



Only one stable compound appears, viz, CaSiOs-MgSiOg, identical with 

 diopside. It melts at 1,380° and has a specific gravity of 3.275. It was ob- 

 tained in well-formed, measurable crystals extremely pure, when crystallized 

 from molten calcium chloride. 



A eutectic occurs between diopside and pseudo-wollastonite at the composi- 

 tion 60 per cent diopside : 40 per cent calcium silicate. It melts at 1,348°. A 

 second eutectic occurs at 68 per cent MgSiO, : 32 per cent CaSiOg. It is 

 composed of about 95.5 per cent of a mix-crystal containing about 62.5 per 

 cent of diopside: 37.5 per cent magnesium silicate, and 4.5 per cent of 

 a-MgSiOg. Its melting temperature is 1,375°. 



Six solid solutions appear in this system. Only two of them contain more 

 than 3 or 4 per cent of the lesser component, and only these will be men- 

 tioned here. 



(a.) iS-calcium silicate (wollastonite) forms a saturated solution contain- 

 ing about 17 per cent diopside (8 per cent MgSiOs) : 83 per cent CaSiOj, 

 when crystallization takes place in the neighborhood of 1,050°, i. e., wollas- 

 tonite is capable of dissolving about §^ = 20 per cent of its own weight. This 

 series of solutions is interesting from the fact that the inversion-point of pure 

 calcium silicate (1,190°) appears to be raised 100° in the most concentrated 

 solutions by the addition of MgSiOo. This is probably largely, if not wholly, 

 an apparent rise in the inversion point due to viscosity, for, as is well 

 known, an inversion-point should be raised only when the concentration of 

 the solution below the point is greater than that above, while here there is a 

 rise in the weaker solutions which suffer no change in concentration when 

 they invert. Again, the concentration of solutions just below the inversion 

 point can not be determined with accuracy on account of the difficulty of es- 

 tablishing an equilibrium in solid silicate solutions. 



(&.) Diopside dissolves about 60 per cent of its own weight, forming a so- 

 lution which contains 66.5 per cent MgSiOg : 33.5 per cent CaSiOg. This 

 saturated solution is very similar to diopside in all its properties. Its melting- 

 point is only 3° lower; the index of refraction and specific gravity are 

 changed very little, both are a little lower, while the optic axial angle and ex- 

 tinction angle were found to fall about 0.5° for each additional i per cent 

 of MgSiOs. 



The specific-volume curve consists of three well-defined branches, the first 

 of which is the locus of the volume of mechanical mixtures of pseudo-wol- 

 lastonite (a-CaSiOs) and diopside; the second, that of the solid solutions of 

 magnesian pyroxene (iS-MgSiOg) in diopside; and the third the locus of the 

 volumes of mixtures of saturated mix-crystals just mentioned, and the free 

 magnesian pyroxene. The volume of the solid solutions is greater than the 

 sum of the constituent volumes. There is a sharp minimum on the curve at 

 the composition of diopside CaSiOg.MgSiOg. On account of the presence of 

 minute bubbles in the crystals and the comparatively small difiFcrence be- 

 tween the specific gravity of diopside and that of the magnesian pyroxene, 

 the critical points on the curve are several per cent in error. 



