186'9.] Mineralogy. 131 



In a paper "On the Distribution of Microscopic Nepheline," * 

 Dr. Zirkel shows that this mineral, which a few years ago was re- 

 garded as pecuHar to an exceedingly limited number of rocks, 

 really enjoys a very wide-spread distribution, but that its crystals 

 are in general so minute as to escape detection without microscopic 

 aid. Nepheline usually occurs in six-sided prisms, and therefore 

 its sections will appear as hexagonal or as rectangular plates, 

 according as the crystals are cut transversely or longitudinally; 

 whilst the rectangular sections will be either oblong or square, ac- 

 cording to the height of the prism. A^Tien pure, nepheline is clear 

 and colourless, but the larger crystals are usually more or less 

 tinted by the presence of numerous grayish particles exceedingly 

 minute, and variously disposed within the substance of the mineral : 

 such particles are often accumulated in the centre of the crystal, and 

 sm'rounded by a j)ellucid zone. When cut parallel to the principal 

 axis of the prism, the sections often exhibit long lines of jjarticle? 

 running in a longitudinal du-ection ; and many of the crystals are 

 also penetrated by tiny needle-like prisms of green augite. In 

 microscopic examination, the observer must beware of mistaking 

 crystals of apatite for those of nej)heline, since the two minerals 

 assume somewhat similar forms. 



Having thus estabhshed the characters of microscopic nepheline, 

 Zirkel proceeds to trace its distribution. Among the principal 

 rocks in which he has detected it, may be mentioned the hornblende- 

 andesite of the Wolkenberg and other hills of the Siebengebii'ge on 

 the Ehine ; the sanidine and oKgoclase trachyte wliich forms the 

 well-known " castled crag of Drachenfels " ; the similar trachytes of 

 the Cantal in Central France ; the famous domite of the Puy-de- 

 Dome ; and many of the trachytes and andesites which form so 

 marked a featm'e in the geology of Hungary and Transylvania. It 

 has long been supposed that certain basalts may contain nepheline, 

 but Zirkel converts this supposition into a certainty : its presence 

 in such rocks is however difficult to determine, and the sections need 

 to be carefully prepared. Our Scotch geologists may not be aware 

 that the greenstone of Arthur's Seat is remarkably rich in well- 

 formed crystals of nepheline. Nor must it be supposed that the 

 presence of this mineral is confined to rocks of any particular geo- 

 logical epoch, since it is found equally in the youngest eruptive 

 rocks and in the oldest melaphyres. 



Two new Silesian minerals have recently been described by Dr. 

 Websky, of Breslau.f One of these is named, from its locaht}'-, 

 Kochelite, whilst the other is to be called Sarcojmde, in allusion to 



* ' Ueber die Verbrcituug mikroscopiscber Nepheline.' Leonharcl und Geinitz's 

 'Neues Jabrbiich fiir Mineralogie,' u.s.w. 1868. Heft VI., p. (J97. 



t ' Ueber Sarkopsid und Kocliellt, zwei neue Minerale aus Schlesien.' Zeit- 

 schrift d. Deutsch. Geolog. Gesellschaft. 1868. Heft II., p. 245. 



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