Minerals of the Composition Mg Si 0^. 387 



more was similar to that from the melt, with the difference that 

 the spherulites and their component fibers were smaller. 



(3.) All other forms of magnesium silicate change to the 

 monoclinic pyroxene by heating to temperatures from 1150° 

 upwards, the temperature depending on the original form and 

 the time allowed. 



(4.) A repetition of Hautefeuille's work proved the correct- 

 ness of his observations except as to the crystal form of his 

 product. Magnesium chloride dissolves amorphous silica in 

 the presence of small quantities of moisture 



(MgCl 2 + H 2 + Si0 2 =MgSiO, + 2HCl) 



but exerts little action on quartz. Instead of the chloride 

 one may use the tellurite, an easily fusible salt which acts as 

 readily on the silica as the chloride, has the advantage of 

 being less susceptible to the action of water, and the disad- 

 vantage of being readily reducible to the metal and attacking 

 the platinum crucible in which the fusion is made. The fol- 

 lowing equation represents the reaction : 



MgTe0 1 + SiO„ = MgSiO, + Te0 4 . 



The tellurous oxide is volatilized at the temperature of the 

 experiment (700°-800°). The crystals obtained by both mag- 

 nesium chloride and magnesium tellurite were generally small 

 and not so well developed as those crystallized by method (5). 

 (5.) A considerable number of fluxes were found to dis- 

 solve magnesium silicate at temperatures of 800°-1000° and to 

 precipitate it again in crystals of the monoclinic variety, a 

 fact which has an important bearing on the question of the 

 relative stability of the different crystal forms. It soon 

 became evident, moreover, that certain fundamental questions 

 connected with the pyroxene series could only be settled by 

 the crystallographic study of the monoclinic form, so that we 

 made a rather extensive investigation of the conditions nec- 

 essary to obtain from these fluxes crystals sufficiently well 

 developed for measurement. Among these solvents which 

 did not prove satisfactory, we may mention calcium chloride, 

 sodium sulphate, sodium chloride and potassium chloride. 

 The last two gave small yields of an unpromising crystalline 

 product which was not fully investigated. The fusible sili- 

 cates of lead, sodium and potassium* all gave glasses. In 

 point of time, we first tried fusible magnesium salts as proba- 

 bly best suited to dissolve the silicate without decomposing it. 

 Of these there are the tellurite, the vanadate and the chloride. 

 With Magnesium Tellurite. — As stated above, the tellurite 

 is a readily fusible salt, and though not soluble in water, it 



* It was found later that a solution of magnesium silicate in a small 

 quantity of sodium and potassium silicates yields good crystals of enstatite. 



