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University of California Publications. [Geology 



bility that all of the carbon in the deposit is from organic 

 matter, the C0 2 of the carbonate escaping, as some of the shales 

 are quite bituminous. 



Structure of the mineral. — The neocolemanite is massive crys- 

 talline with a very glassy luster and eminent clinopinacoidal 

 cleavage. It has also a distinct basal cleavage, yet does not part 

 readily in this direction. This basal cleavage can be seen as 

 lines on the clinopinacoid and is a very important help in the 

 proper orientation of the crystals, because the angles for the 

 positive faces are quite similar to those for the negative. The 

 clinopinacoidal cleavage is so prominent that practically all of 

 the mineral comes from the mine in cleaved fragments and 

 cleaved masses. Specimens with a divergent columnar structure, 

 the columns curving into fan-like shapes, are frequently found. 

 A peculiar fibrous form of the lime borate with a satin luster 

 occurs in the main shaft, which strongly resembles satin-spar. 

 Crystals are comparatively rare and only a few good specimens 

 were obtainable. 



Crystal habits. — The crystals occur thickly grown together 

 and firmly attached to the massive mineral. In general they are 

 so attached that either the right or left half of the crystal can 

 be seen. They range from several millimeters to more than a 

 centimeter in width. Three distinct habits occur, each on a dis- 

 tinct type of the massive material. Crystals of Habit 1 are large, 

 white, and translucent, lining the inner surface of a geode. They 

 are the simplest type of the crystals, consisting mainly of the com- 

 bination of the unit prism (110) and the clinodome (Oil). This 

 habit is shown in figure 1, plate 30. Habit 2 is more common. 

 The crystals are pale brown and nearly transparent, and possess 

 the largest combination of forms. The predominating forms are 

 the unit prism and clinodome, like in Habit 1, but the ends of 

 the 5-axis are invariably terminated by a group of small faces, as 

 seen in figure 2. A more general combination of forms on this 

 type is shown in figure 3. Habit 3 is totally dissimilar to the 

 others. The crystals are white or colorless, occurring in small 

 cavities in a white and coarsely granular variety of the mineral. 

 In this habit the unit prism is elongated vertically and terminated 



