THE BARITE DEPOSITS OF MISSOURI 61 



masses whose surfaces are covered with small, more or less di- 

 vergent crests. Upon these there are still other very small groups 

 of crests, usually about an eighth of an inch long. These cone- 

 shaped masses are large and commonly weigh 200 pounds or 

 more. (PI. VII, A.) They are nearly always found adjacent 

 to the dolomite. Many of the massive pieces contain small cavi- 

 ties lined with crested crystals. The size of the tabular plates in 

 the various masses varies widely. In some of the small concre- 

 tionary masses they are so small that the barite has an almost 

 granular appearance, while in others the blades of the crests are 

 several inches long. The so-called "chalk-tiff" is a finely gran- 

 ular, porous variety of barite. "Ball-tiff" is concretionary barite 

 which is finely crystalline, but in which the tabular faces are 

 curved. 



Crystals of barite were found in only four or five places in 

 the Washington County district. Many small but perfect crystals 

 were found at the Eye mine. They occurred in a red clay. On 

 the southwest quarter of Sec. 29, T. 38 N., R. 2 E., clusters of 

 rather large but simple crystals were found. In the Central dis- 

 trict crystals weighing several pounds were found in red clay in 

 a cave at the Wilson diggings near Henley. (PI. IV, D.) They 

 were all comparatively simple. The private collection of Mr. F. 

 A. Sampson of Columbia, Missouri, was studied, but this also 

 is composed of comparatively simple forms. Most of Mr. Samp- 

 son's collection came from the Central district where especially 

 fine crystals have been found. In the collection of the University 

 of Missouri, there are many specimens of the unique barite crys- 

 tals from Pettis County, Missouri, which have a white or opaque 

 border, often nearly an inch wide (PI. IV, E.) around a trans- 

 parent to translucent interior. This white border was analyzed 

 by Luedeking and Wheeler^ and found to have the following 

 composition : 



BaSO^ 87.2% 



SrSO, 10.9% 



CaSO^ 0.2% 



(NHJ2SO4 0.2% 



H2O 2.4% 



'Luedeking, Charles, and Wheeler, B. A., Am. Jour. Sci., 3d series, 

 vol. 42, p. 495. 



