140 



University of California. 



IVOL. 3. 



covered with botryoidal chalcedony, from which depend slender 

 stalactites of the same mineral. The floor is built up of several 

 variegated layers of chalcedony and opal, and a change of position 

 during its formation is prettily shown by the fact that the upper 

 half of the layers is inclined at an acute angle to the lower 

 layers. 



A second geode contains a lining of chalcedony, while the 

 centre is quite filled in with small granular crystals of pale lilac 

 and apple-green tints, of fiuorite. The identity of the mineral 

 was proved by its form, its isotropic behavior toward polarized 

 light, and the evolution, on treatment with sulphuric acid, of 

 hydrofluoric acid fumes. The writer has seen no mention of a 

 similar occurrence of fiuorite. 



In another hollow spherulite, the cavity was first lined with 

 chalcedony and a little milky opal, then almost filled with a snow- 

 white mineral compact near the inclosing wall, but finely fibrous 

 in the centre. Inclosed in the compact portion of this sub- 

 stance, in much smaller amount, are many small lustrous tablets 

 of a bright orange-red color. 



The fibrous mineral was found to have the following proper- 

 ties: Heated in the closed tube, it gives off abundant water. 

 Before the blowpipe it fuses at about 3 J to a white enamel. 

 Boiled with strong acids, it dissolves but sparingly, and does not 

 gelatinize. Of the optical properties little could be ascertained, 

 because of the extreme slenderness of the fibres, but it was found 

 that the extinction is straight, the elongation parallel to the axis 

 a, and the double refraction weak. The mineral readily dis- 

 solves in hydrofluosilicie acid, and the solution deposits, on 

 evaporating, hexagonal crystals of sodium fluosilicate, and 

 amorphous fluosilicate of aluminum. We therefore have, evi- 

 dently, a soda zeolite, but one with properties differing from 

 those of auy described mineral. 



The red tablets also appear to be of a zeolite with soda as the 

 base. There is a perfect cleavage parallel to the tabular face, 

 and cleavage flakes examined in convergent polarized light are 

 found to be normal to a positive, probably acute, bisectrix. The 

 red color is clue entirely to disseminated particles of ferric oxide. 

 Before the blowpipe, the mineral exfoliates, swells and easily 



