280 REPORT OF NATIONAL MUSEUM, 1899. 



OcGurreTice. — According to Dana the mineral occurs at Strontian in 

 Argyllsiiire, in veins traversing gneiss, along with galena and barite; 

 in Yorkshire, England; at the Giants Causeway, Ireland; Clausthal, in 

 the Harz; Briiunsdorf, Saxony; Leogang, in Salzburg; near Brix- 

 legg, Tyrol; near Hanim and Minister, Westphalia. In the United 

 States, at Schoharie, New York, in the form of granular and columnar 

 masses and also in crystals, forming nests and geodes in the hydraulic 

 limestone; at Clinton, Oneida County; Chaumont Bay and Theresa, 

 Jefferson County; and Mifflin County, Pennsylvania. 



Uses. — Strontianite, so far as the writer has information, has but a 

 limited application in the arts. It is stated^ that '" basic bricks" are 

 prepared from it by mixing the raw or burnt strontianite with clay or 

 argillaceous ironstone in such proportions that the brick shall contain 

 about 10 per cent of silica, and then working into a plastic mass with 

 tar or some heav}^ hydrocarbon. After molding, the bricks are 

 dusted with fine clay or ironstone, dried, and burned. The effect of 

 the dusting is to form a glaze on the surface, which protects the brick 

 from the moisture of the air. Like celestite, it is also used in the pro- 

 duction of the red lire of fireworks. The demand for the material is 

 small, and the price but from $2.50 to $4 a ton. 



6. Rhodochrosite; Dialogite. 



This is a pure manganese carbonate of the formula MnC03,= carbon 

 dioxide, 38.3 per cent; manganese protoxide, 61.7 per cent. The color 

 is much like that of rhodonite (see p. 314), from which, however, it 

 is readily distinguishable by its rhombohedral form, inferior hard- 

 ness (3.5 to 4.5), and property of dissolving with effervescence in hot 

 hydrochloric acid, while rhodonite is scarcely at all attacked. The 

 mineral is a common constituent of the gangue of gold and silver 

 ores, as at Butte, Montana; Austin, Nevada, etc. (Specimen No. 26745, 

 U.S.N.M.) So far as known the mineral has as yet no commercial 

 value. 



7. Natron, the Nitrum of the Ancients. 



This is a hydrous sodium carbonate; Na2CO3+10H2O, = carbon 

 dioxide, 15.4 per cent; soda, 21.7 per cent; water, 62.9 per cent. 

 Occurs in nature, according to Dana, onl}^ in solution, as in the soda 

 lakes of Egypt and elsewhere, or mixed with other sodium carbonates. 

 The artiticially crystallized material is of white color when pure, soft 

 and ^brittle, and with an alkaline taste. Crystals, thin, tabular, 

 monoclinic. Thermonatrite, also a hA'-drous sodivim carbonate of the 

 formula NaoC03+ 11^0= carbon dioxide, 35.5 per cent; soda, 50 percent, 

 and water 14.5 per cent, occurs under similar conditions, and is con- 

 sidered as derived from natron as a product of efflorescence. (See 

 further under Sodium sulphates, p. 405.) 



^ Journal of the Society of Chemical Industry, III, 1884, p. 33. 



