OusACK — On the Melting Points of Minerals. 405 



for by the fact that it is nearly impossible to reduce a fibrous substance 

 to powder ; its appearance under the microscope resembles particles of 

 finely chopped hay rather than a dust. Actinolite is viscous, but it is 

 possible to determine a point at which it is decisively melted ; in fact 

 all the silicates present a period of viscosity in a greater or less degree, 

 so that none of them can be said to melt at any definite temperature, 

 but one can say a substance is melted at this temperature, and is not 

 at that. The difference between the two temperatures is never more 

 than about 10°, so that leaving a margin of 5° on either side of 

 the temperatures given, the substance may be said to melt witbin 

 that range, except in very exceptional cases, which are especially 

 mentioned. 



Tremolite. — The two specimens were to all appearance similar, and 

 behaved the same as actinolite. 



Hornblende undergoes a short period of viscosity which is only 

 perceptible with difficulty. 



Diopside. — The specimens examined were all transparent, two were 

 of a pale green, the other was nearly white ; their behaviour was 

 similar to hornblende. 



Biallage — Different specimens of this mineral varied very much as 

 to their melting points, more so than any other mineral examined, but 

 this has been remarked on elsewhere. The period of viscosity varies 

 with different specimens, and the way the substance is ground was 

 also found to affect the melting point ; only after the greatest difficulty 

 was it reduced to a sufficiently fine powder to obtain the results 

 given ; the previous results with the same specimens were very much 

 higher. 



Augite is not distinguishable from hornblende on the ribbon. 



Spodumene behaves rather like the felspars, and has to be reduced 

 to the very finest dust ; it bubbles at about 1200° C. 



WoUastonite. — Both specimens were white, and presented fibrous 

 structure ; their viscosity was hardly observable. 



Endatite. — A specimen of the variety Bronzite was observed to be 

 viscous at about 8° below its melting point, which is slightly more 

 than is the case of most minerals. 



Olivine is the most viscous mineral met with ; one specimen was 

 viscous at 1323°, and only fiowed freely at 1407°, but after careful 

 observation it was found to be melted at 1378°, but to retain a globular 

 form, which was hard to distinguish from the surrounding dust, as 

 only the very smallest particles are seen to melt at this temperature. 

 If the larger particles are watched on the ribbon it will be seen that 



