408 Progress in Science. [July, 



of the presence of mercury in the metallic coating or deposit on the copper, 

 and is equally applicable should there exist in that deposit a combination of 

 mercury with any or all of the other three metals which yield by Reinsch's 

 process a metallic deposit on copper foil. 



MINERALOGY. 



At present we are in great measure ignorant of the conditions which are 

 necessary for determining the appearance of certain faces in a crystal. 

 Chemical research has, indeed, afforded some insight into this subject; we 

 know, for instance, that alum may be made to crystallise in cubes by the pre- 

 sence of alkaline carbonates ; in octahedra by the presence of sodic nitrate ; 

 and in a combination of the two forms by the presence of cupric nitrate. In 

 the case of most native crystals, however, the subject is still so obscure that any 

 attempt at its elucidation must needs be welcome. Dr. A. Stelzner, of 

 Freiberg, who has, we believe, been recently appointed Professor of Mineralogy 

 in the University of New Cordova, publishes a memoir, in which he seeks to 

 discover what natural causes have induced the presence of trapezohedral 

 planes in certain crystals of quartz.* Compared with the ubiquity of quartz 

 the appearance of these faces is extremely rare. The author collects all the 

 known instances of their occurrence, and records the accompanying minerals, 

 with their relative age. These paragenetic studies show that the minerals 

 associated with trapezohedral quartz are chiefly apatite, axinite, datholite, 

 fluor-spar, mica, topaz, tourmaline, beryl, scheelite, iron-glance, anatase, 

 rutile, brookite, sphene, wolfram, and cassiterite ; and that the quartz must in 

 general have crystallised nearly contemporaneously with these substances. 

 As many of these associated minerals contain compounds of fluorine, chlorine, 

 or boron, the author deduces the conclusion that the presence of these 

 elements must be connected with the trapezohedral habit of quartz. More- 

 over, it is found that small faces of this form may be developed on quartz by 

 etching the surface with hydrofluoric acid. The author's studies lead him to 

 the general conclusion that the trapezohedral form of quartz is restricted 

 to those cases in which the crystals have been formed contemporaneously 

 with certain minerals of the tin or titanium formation, with development 

 of hydrochloric or hydrofluoric acid. 



Mr. Robert H. Scott, of the Meteorological Office, has presented to the 

 Geological Society some notes on the interesting group of minerals found in 

 the mines of Strontian, in Argyllshire. This locality, which gives its name to 

 the element Strontium, contains several lead-mines, which yield many rare 

 zeolitic minerals, especially harmotome and Brewsterite. The former has been 

 found chiefly at Bell's Grove Mine, and the latter at Middle Shap Mine, 

 whilst both of them have been obtained from Whitesmill Mine. At the newly- 

 opened workings at Corrantree, fine crystals of calcite occur in association 

 with well-twinned crystals of harmotome. The mine is opened in gneiss, 

 whilst the old mines were worked at the junction of the gneiss with the 

 granite. In all these workings the gangue is remarkable for the absence of 

 fluor-spar, and the comparative rarity of zinc-blende and barytes ; whilst the 

 galena is but slightly argentiferous. 



Eosite is the name which Dr. Schrauf has applied to a new mineral from 

 Leadhills, in Scotland. It occurs in small aurora-red octahedra, sparsely 

 scattered over the surface of a greenish-yellow cerussite, and accompanied by 

 very small yellow needles of pyromorphite. The new species crystallines in 

 the pyramidal system, and contains molybdenum, vanadium, and lead, 

 forming a connecting-link between wulfenite and vanadinite, and yet essen- 

 tially different from the well-known forms of red wulfenite. The name has 

 reference, we presume, to the aurora-red colour of the crystals. 



A new mineral discovered by the distinguished geologist, Dr. Giimbel, 

 has very properly received the name of Giimbelite. It is a hydrous silicate of 



* Quarz und Trapezoederflachen : eine paragenetische Skizze. Leonhard u. Geinitz's 

 Neues Jahrbuch, Heft i., 1871, p. 33. 



