350 University of California Publications in Geology [Vol. 10 



the &-axis as usual, and they show striated domes with the cleavage 

 base, but no end-faces. 



Quartz. — Specimens of compact granular quartz rock found in the 

 talus of the Commercial Rock quarry indicate that seams of quartzite 

 were formed in the crystallized limestone by its metamorphism. It is 

 quite possible that sandstone seams occurred in the original formation 

 and that these have been the source of much of the silica necessary to 

 form such an abundance of silicate minerals. Quartz is a minor con- 

 stituent of the igneous rocks and occurs in the usual smoky-brown 

 color. Small druses of the mineral are occasionally found, but large 

 crystals are rare. 



Tourmaline. — Boron is a characteristic element in the rocks of 

 Southern California and practically all of the pegmatites of that 

 region carry boro-silicates, especially tourmaline. Three of these boro- 

 silicates have been observed in the pegmatites of Sky Blue Hill and 

 a few specimens have been collected, but the writer is without any 

 data concerning them. 



The tourmaline is black columnar and occurs sporadic in the 

 pegmatite. 



Axinite. — Violet-colored axinite associated with cinnamon-garnet 

 occurs in large fragments in the pegmatite. Bright crystal faces, often 

 striated, occur but crystals are not complete enough to measure. 

 Axinite appears to be common in this particular region, as it is 

 abundant at the Riverside quarry and has been noted in other places 

 in the vicinity. Rogers 8 has described a large crystal from Riverside. 



Datolite. — Glassy white datolite with slightly greenish tinge occurs 

 in connection with the pegmatites. The specimens sent to the writer 

 are compact massive. 



Seapolite. — Specimens of seapolite were recently collected by 

 Chilcls. The mineral is in close association with green pyroxene, 

 quartz, feldspar, wollastonite, and grossularite garnet. The color of 

 the seapolite is grayish white, but it contains violet-blue streaks. The 

 variety is probably wernerite. 



Apophyllite. — The masses of wollastonite which have formed on the 

 contact between the pegmatites and limestone contain cavities lined 

 with small crystals of apophyllite. The crystals are colorless to white 

 and are usually closely interlocked. Two habits are prominent; one 

 is the common cubo-octahedral type with small faces of the pyramid 

 and the base and second-order prism about equal in size. The other 



s School of Mines Quar., vol. 33, p. 373, 1912. 



