484 Journal of Applied Microscopy. 



Si03,MeR2SiOe, and Me^RoSi^Oi o (Me = Ca, Mg, Fe Na.,; [Rg = AU Fe2). 

 The MeR^SiOg can form independently apparently as a rhombic pryoxene. 

 In acid magmas the MeSiOg preferably unites jwith the MoR^Si^O^j) ^^^ ^^ 

 more basic with Me. RgSiOg. In magmas containing about 50 per cent. SiOr,, 

 rhombic pyroxene forms if the ratio of MgO + FeO to CaO is equal to or 

 greater than 3, if the ratio is notably less, monoclinic pyroxene separates. 



Over 30 species are described, the methods of examination detailed, and 

 photo-cuts given of the crystals obtained. a. j. m. 



Von Federow, E. Ueber Krystallzeichnen. This article is designed to supplement 

 Zeit. f. Kryst. 30: o, i8q8. ^i,,-i, ,,*r 



Goldschmidt s method* of construction 



of clinographic projections from the gnomonic projjection without using crystal 



axes. A. J. M. 



Von Federow, E. Ueber Isomorphismus. Zeit. f. Kryst. 30: 17-22,1898. 



Diamond Saw (Improved Pattern). Made by Saws 6 to 10 inches in diameter can be 

 Chas. L. Whittle, 7 Exchange Place, Bos- adjusted tO any ordinary lathe, and 

 ton, Mass. Catalosrtie circular. , ,. . . , 



complete directions are given for use 

 and speed of rotation. A 6-inch diameter saw, properly handled, should cut 

 300 to 400 square inches of average rock and much more of limestone, etc. 

 Price: 6 in. saw, $5.00; 12 in, saw, $10.00. l. McI. l. 



n . . n 1 ei- • ». I.- t , Cuts unusually large planes (2 to 4 sq. 



Petrotome or Rock Slicing Machine. Invented . . . 



by \Ym. B. Dwight, and made by C. H. inches) of sections in any required 

 Cowdrey Machine Works, 5 Main st., direction, or series of parallel planes. 



1" Itch burg, Mass. Catalogue circii/ar. _ . 



By special accessory apparatus a series 

 of parallel planes can be cut in a single operation. Trims large cabinet speci- 

 mens very conveniently. Detailed description and cut given. Price, $200.00. 



L. McI. L. 



INDIVIDUAL SPECIES. 



Augelite from a new locality in Bolivia. L. J. Occurs sparingly in veta (vein) carmen 

 Spencer. Min. Mag. 12: i, i8g8. ^ • -i • rr^ • 1 t^ ^ 



^ of the silver mines at Tatasi and Port- 



ugalete, Sud-Chicas, Dept. Potosi. Colorless and transparent, showing usual 

 perfect cleavages, and generally imbedded in massive pyrite. Closely resem- 

 bles barite. Forms of observed crystals given. Indices of refraction for Na 

 light, 1.5752 and 1.5893. 2 E = 82i^°. G. = 2.09. l. McI. l. 



Argyrodite (stanniferous) from Bolivia: The Found at AuUagas, Chayanta, Dept. 

 identity of the so-called "Crystallized t^ . n 1 n 1 1 1 • 



Brongniardite " with Argyrodite-Canfield- PotOSl, as small, dull black, isonietric 

 ite. G. T. Prior and L. J. Spencer. Min. crystals encrusting pyrargyrite. Inter- 

 Mag. 12: s, 1808. . ,, , • n 



esting crystallographically on account 



of the twinning, and chemically in giving a different ratio of Sn and Ge from 

 that found in original canfieldite. Composition = 5 (4 Agg S. Ge S._,) -p 2 

 (4 Ag2 S. Sn 83). G.=6.19 at 18° C. 



Also found to be identical with the cubical crystals referred by Damour to 

 brongniardite (proved by chemical and physical re-examination of the latter 

 mineral). 



The occurrence of tin ores in Bolivia (according to Stelzner) is peculiar, 



*Zeit. f. Kryst. 19: 352, 1891. 



