Scientific Intelligence — Geology and Mineralogy. 187 



parency vary like the cleavage, and that the plane-angles at tlic sum- 

 mit are often unequal. — {American Journal of Science and Arts, 

 New Series, vol. v.. No. 15, May 1848, p. 419.) 



13. M. Ebelmen on Artificial Hyalite and Hydrophane. (Aca- 

 demy of Sciences, Dec. 4, 1847, L'Institut, No. 727.) — About two 

 years since, Ebelmen presented to the Academy several products ob- 

 tained by exposing silicic ether to moist air ; one of these is as trans- 

 parent and colourless as quartz-crystal ; the others have an opaline 

 tint, but in water they become as transparent as native hydrophane. 

 The specimens now presented were of much larger dimensions, and 

 are in the form of hemispherical lenses obtained in glass-globes ; they 

 have remained entire, notwithstanding the considerable shrinkage 

 which they have suffered. One of these lens-shaped masses is 5 or 

 6 centimetres in diameter ; it has hardened during five or six months, 

 and the molecular movement in it has not yet ceased. 



In mixing silicic ether with coloured alcoholic solutions, various 

 tints of colour are imparted to the product. One of the most re- 

 markable of these effects is from the employment of chloride of gold, 

 which colours the silica of a beautiful topaz-yellow. After a time, 

 and under the influence of diffuse light, flakes of gold, with the me- 

 tallic lustre and brilliancy, are developed in the midst of the solid 

 mass, giving it the appearance of aventui-ine. The development of 

 metallic plates, in the midst of a solid mass, is a very remarkable 

 molecular phenomenon, the study of which cannot fail to be of interest 

 in explaining the origin of natural aventurine. Exposure to the di- 

 rect light of the sun colours the aventurine of chloride of gold, of a 

 blue violet or rose colour, remaining quite transparent. Thus, by 

 the humid mode, we can reproduce the rose colour which is imparted 

 by the dry mode to glass by gold. When the crystals of gold, pro- 

 duced in the midst of the siliceous mass, are very numerous, a green 

 colour can be observed in it by transmitted light. 



The diaphanous silica obtained by silicic ether, may be compared 

 to the hyalite of mineralogists, which possess no double refraction. 

 Hyalite is much hardei*, and the amount of water it contains does 

 not exceed j\%, whilst the product obtained by M. Ebelmen con- 

 tains 22 per cent, of water. The artificial product, however, con- 

 tinues for a long time to lose water under the influence of a very 

 gentle molecular change. The author has observed that, after more 

 than two years' exposure to air, the product contains not more than 

 19 per cent, of water; dried at 115° C, the diaphanous silica loses 

 its water and becomes slightly opaline. It regains several centimes 

 of this water by further exposure at the common temperature, but 

 without recovering its transparency. 



14. Geoloijy of the Coasts of Australia. By J. Becte Jukes, 



