Sl'llERi:T.lTr<:S AND LITITOPTIYS.K 



269 



tridymite, can not be determined from the data available. The presence 

 of tridymite is not decisive evidence of a temperature of formation al)ove 

 870°, for Fenner^^ has shown that it may crystallize as a metastable 

 phase at relative low temperatures, especially in the presence of fluxes. 



In sonae of the outer cavities a later ferruginous staining has been in- 

 troduced, ])ut this does not extend into the rock for anv distance, as is 



FiGtjisE G. — Remarkable Lithophysw in Oisidian 

 Cube-shape oavity. Specimen 88431. Two-thirds natural size 



evident from tbc fact tbat the cavities on a iVesldy I'ractiii-ed surrafc do 

 not show the slightest trace of such staining. 



To recapitulate: Specimen 884.30 proves detinitcly tliat crystallization 

 of radial spherulites took place as a result of the action of gases at high 

 temperatures, at wliidi tiie obsidian was still soft and capable of flowing 

 into fa\iti<'s whicb bail been sheared or had collapsed to a slight extent. 

 'J'br L-\ idencr of tbc presence of volatile components at high temperatures 



I' .\in. .lour. s.i. lii. vol. :;i;. r.u:;, pp. .•{;n-.s.s4. 



