412 REPORT OF NATIONAL MUSEUM, 1899. 



masses, and in radiating- fibrous masses in the Laurentian formations 

 about Renfrew. Large crystals of a red color are also found in 

 Brown Count}^, Kansas, and at Lampasas and near Austin, Texas. 

 (Specimen No. 67936, U.S.N.M.) Near Bells Mills, Blair County, 

 Pennsylvania, the mineral occurs in lens-shaped masses between the 

 bottommost beds of the Lower Helderberg (No. VI) limestone. On 

 South Bass Island, in Put in Bay, Lake Erie, the mineral occurs fre- 

 quently in the form of lieautif ul crystals of all sizes up to 100 pounds 

 in weight, transparent to translucent and sometimes of a fine blue 

 color, lining the walls and floor of limestone caverns. 



Uses. — Celestite is used in the preparation of nitrate of strontia 

 employed in fireworks, its value for this purpose being due to the fine 

 crimson color it imparts to the flame. The demand for the material is 



very small. 



4. MiRABiLiTE or; Glauber Salt. 



This is a hydrous sodium sulphate, Na^SOi+lO H20, = sulphur 

 trioxide, 24.8 per cent; soda, 19.3 per cent; water, 55.9 per cent. In 

 its pure state white, transparent to opaque; hardness, 1.5 to 2; specific 

 gravity, 1.48. Readily soluble in water, taste cool, then saline and 

 bitter. 



Occurrence. — Aside from its occurrence in soda lakes associated with 

 other salts as described later this sulphate is of common occurrence 

 as an efiloresence on limestones, and in protected places, as in Mammoth 

 Cave, Kentucky, may accumulate in considerable quantities, though not 

 sufficient to be of economic value. (Specimen No. 68156, U.S.N.M., in 

 Cave series.) Salt Lake, Utah, contains a proportionately large 

 amount of this sulphate, which during the winter months is precipi- 

 tated to the bottom, whence it is not infrequently thrown upon the 

 shore by waves. 



According to Prof. J. E. Talmage/ when the temperature falls to a certain point, 

 the lake water assumes an oj^alescent appearance from the separation of the suljihate. 

 This sinks as a crystalline precipitate and much is carried by the waves upon the 

 beach and there deposited. Under favorable circumstances the shores become cov- 

 ered to a depth of several feet with crystallized mirabilite. The writer has on several 

 occasions waded through such deposits, sinking at every step to the knees. Speak- 

 ing only of the amounts thrown upon the shores, and of most ready access, the source 

 is practically inexhaustible. The substance must be gathered, if at all, soon after 

 the deposit first appears; as, if the water once rises above the critical temperature, 

 the whole deposit is taken again into solution. This change is very rapid, a single 

 day being oftentimes sufficient to effect the entire disappearance of all the deposit 

 within reach of the waves. Warned 1>y these circumstances, the collectors heap the 

 substance on the shores above the lap of the waters, in which situation it is compar- 

 atively secure until needed. To a slight depth the mirabilite eflBloresces, but within 

 the piles the hydrous crystalline condition is maintained. At the present time there 

 are thousands of tons of this material, heaped in the manner described, remaining 

 from the collections of preceding winters. The sodium sulphate thus lavishly sup- 



' Science, XIV, 1889, p. 446. 



