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University of California Publications in Geology [Vol. 10 



causing the change from periclase to brucite. Graphite was not promi- 

 nent in the quarries on Sky Blue Hill. 



Phlogopiie. — A few flakes of brown phlogopite mica nave been 

 observed in the white limestone of Chino Hill. 



Serpentine. — Very little serpentine has been found on either hill. 

 A few small patches and streaks occur here and there in the white 

 marble of the Chino quarry. 



MINERALS IN THE CONTACT ZONES OF SKY BLUE HILL 



Blue Calcite. — The blue calcite occurs only in the Commercial Rock 

 quarry. Some of it is intensely blue, especially when freshly exposed, 

 but it fades somewhat to more of a sky-blue color. It does not occur as 

 one large mass of blue calcite, but rather as seams, bands, and patches 

 intimately mixed with the various metamorphic minerals. When the 

 quarry was first opened the blue calcite was very common and was 

 used for road rock and in sugar refining, but very little is now seen. 

 It is one of the contact metamorphic minerals ; and in the recrystal- 

 lization of the carbonate larger rhombohedrons have resulted, some of 

 the cleavage rhombohedrons measuring four to five centimeters in 

 diameter. The cause of the blue color has not been determined, but is 

 believed to be due to minute inclusions of carbonaceous matter. Slight 

 heat completely decolorizes it. This blue calcite forms the matrix for 

 wilkeite, crestmoreite, xanthophyllite, and monticellite, and contains, 

 besides, minute crystals of vesuvianite and diopside. Pale green and 

 pale pink specimens of calcite are occasionally seen, but the prevailing 

 colors are blue and white. 



Wollastonite. — The calcium silicate has been most abundantly 

 formed in the limestone, especially on Sky Blue Hill. It forms great 

 masses in the North Star quarry and tons of it can be obtained. Four 

 structural types or habits may be ascribed to the Crestmore wollas- 

 tonite. 



The first has the common reticulated columnar and fibrous struc- 

 ture which is so characteristic of wollastonite. Crystals of this type 

 are long, narrow and much striated, and generally show no end-faces. 

 Masses of this kind of wollastonite have occasionally been encountered 

 in the limestone of the Chino quarry. 



The second type is represented by large well-formed crystals having 

 the forms and habit of the usual wollastonite crystals. Glassy white 

 crystals, several centimeters long and more than a centimeter broad, 



