ABSTEACTS: MINERALOGY 179 



tallization of the second type occurred in many of the mixtures, whereas, 

 if equihbrium is to be studied, crystalHzation of the first type must be 

 obtained. 



In the optical part of the paper the optical properties of the various 

 crystalline phases are given. The properties of the series of monoclinic 

 pyroxenes extending from diopside to enstatite vary continuously with 

 composition. The artificial pyroxenes are compared with the enstatite- 

 augites of Wahl. 



In considering the bearing of the results on petrologic problems at- 

 tention is called to the resorption of the olivine forsterite in the arti- 

 ficial mixtures and its probable relation to resorption of olivines in nat- 

 ural rocks. The consequences of the possible settling of crystals in a 

 fluid magma (crystallization-differentiation) are discussed in the light 

 of the facts known concerning the artificial mixtures. N. L. B. 



MINERALOGY. — Hewettite, metahewettite, and. pascoite; hydrous cal- 

 cium vanadates. W. F. Hillebrand, H. E. Merwin, and Fred. E. 

 Wright. Proc. Am. Phil. Soc, 53: 31-54. 1914. 



Two apparently different calcium vanadates are described, which 

 resemble each other very closely and have the same composition 

 (CaO • 3V2O5 • 9H2O) when holding their maximum water-content at 

 room temperatures. One of them, hewettite, occurs at Minasragra, 

 Peru, and has been noticed on a single specimen from Paradox Valley, 

 Colorado. The other, metahewettite, occurs at numerous localities in 

 western Colorado and eastern Utah. Both minerals are sparingly solu- 

 ble in water; 



A third calcium vanadate, pascoite (2CaO • 3V205- 11?H20,) is 

 also described. This occurs with hewettite at Minasragra. It is very 

 soluble in water. 



The first and second minerals are regarded as dehydrated acid hexa- 

 vanadates (CaH2VcOi7 • 8H2O), the third as a normal hexavanadate 

 (Ca2V60i7-ll?H20). 



The reasons for specific separation of hewettite and metahewettite 

 are set forth in detail. The two minerals are so sensitive to changes in 

 atmospheric humidity that their water-content varies within wide limits 

 at different times of the year. The removal of all or nearly all the water 

 does not result in breaking down of the crystal structure, and until 

 this has occurred the water is wholly or in great part taken up again 

 when opportunity is ofi"ered. 



The importance is emphasized of bringing all minerals that behave in 

 this way to a definite maximum water-content before analyzing them 



