132 Progress in Chemistry, [January, 



Some simple experiments of considerable interest to the mineralogist have 

 been made by Herr Credner. in Kolbe's laboratory at Liepzig,* with the view 

 of determining what influence is exerted upon the crystalline form of carbonate 

 of lime by the addition of certain substances to the solution from which it 

 crystallises. It is generally believed that aragonite is deposited at high and 

 calcite at low temperatures, but Credner finds that aragonite may be obtained 

 from a cold solution of bicarbonate of lime, if a small quantity of bicarbonate 

 of strontia be present; and that on adding very slowly the strontium 

 bicarbonate to the lime solution, the rhombohedra of calcite which are deposited 

 are accompanied by short acicular crystals of aragonite. The dimorphism of 

 calcic carbonate is seen, therefore, to depend not only on temperature, but also 

 on the presence of foreign substances in the mother-liquor. Again, while 

 calc-spar crystallises in rhombohedra from a pure solution, these simple forms 

 are much modified by the presence of a small proportion of nitrate or carbonate 

 of lead, or of silicate of potash or of soda. 



A specimen of obsidian, or volcanic glass, from Hecla, in the mineralogical 

 collection of Zurich has recently been made the subject of careful microscopic 

 examination by Professor Kenngott.f These observations may be said to 

 supplement those of Zirkel on a like subject. Kenngott's specimen exhibits a 

 brown vitreous base, in which may be detected a number of dark-coloured 

 concretions, each surrounded by a pale ring formed of yellow acicular crystals 

 arranged in a radiate form, whilst certain other smaller concretions are 

 surrounded by fine black hair-like bodies. A few minute crystals of belonite 

 were observable, and throughout the whole base were abundantly strewn 

 certain small black particles, which are probably crystals of magnesian mica. 

 Two parallel layers run across the specimen, and exhibit oblique striation ; 

 the striae may be resolved by a high power into a system of markings, the 

 ultimate lines being merely rows of points which are really small crystals. 



The joint work of Professor Maskelyne and Dr. Flight contains much that 

 is valuable, both chemically and crystallographically ; but as it has been 

 submitted to the Chemical Society, we need do no more in this place than call 

 the attention of the crystallographer to the interesting example of hemi- 

 morphism — not hemihedrism — presented by the crystals of cronstedtite which 

 have recently been found in Cornwall. 



A number of newly-described species and varieties, as usual, call for attention, 

 but must be noticed as briefly as possible. Rionite is the name of a bismuthic 

 variety of fahl-ore from near Cremenz, in the Einfischthal, in Switzerland, 

 where it is worked for the sake of the bismuth which it contains and which 

 amounts to upwards of 13 per cent. \ A manganese ore containing lithium 

 was discovered some time ago by Herr Frenzel, and has been lately described 

 under the name of Lithiophorite.\\ It occurs in some of the iron-lodes of the 

 Erzgebirge, in Saxony, and is merely a product of alteration, derived probably 

 from psilomelane. Professor C. U. Shepard calls attention to some new 

 minerals from the guano deposits in the Guanape Islands. § One of these, 

 termed Guanapite, contains sulphate of potash with sulphate and oxalate of 

 ammonia ; whilst a second species, named Guanoxalite, contains sulphate of 

 potash, oxalate of ammonia, and water. Ambrosite is Shepard's name for a 

 resin resembling amber, and occurring in the phosphatic formation near 

 Charlestown, South Carolina. In compliment to the Tyrolese geologist, Herr 

 Trinker, a new mineral resin, allied to Professor Church's Tasmanite, has been 

 described by Tschermak under the name of Trinkerite.% It occurs in red or 

 brown masses in the lignite of the fresh-water beds near Carpano in Istria, 

 and has the following percentage composition : — Carbon, 8i*i ; hydrogen, 11*2; 

 sulphur, 47 ; and oxygen, 3. Uranotile is Boricky's name for a new mineral 



* Leonhard's Jahrbuch, 1870, p. 603. 



+ Ibid., 1870, p. 529. 



t Ibid., 1870, p. 590. 



II Journ. f. Prakt. Chemie, 1870 ; Bd. 2 (N.S.), p. 203. 



§ "The Rural Californian," Silliman's Journal, Sept., 1870, p. 273. 



IT Jahrb. d. Geol. Reichsanstalt, xx., p. 279. 



