Dec, 1908. Mineralogical Notes 153 



crystals in a parallel direction than the development of a single crystal. 

 Nevertheless many of the planes give reflections like those of a single 

 plane. The color of these crystals is a dark olive-green and they 

 usually exhibit a radiated arrangement in their attachment. The 

 individual crystals are attached by the end of the brachy-axis, their 

 length averaging about 5 mm. The planes are as a whole bril- 

 liant and give fair reflections. Fig. 5, PI. LII, represents a habit 

 tabular with respect to a (100) . This habit is exhibited by the crystals 

 of a single specimen, Mus. No. M 9403. These crystals are very small, 

 their greatest length being .5 mm. and thickness .1 mm. They are 

 also peculiar in being nearly transparent and having a pale olive- 

 green color rather than the deep green to black usually characteristic 

 of the mineral. The cavity in which the crystals occur is lined 

 with chrysocolla, and upon this the olivenite is implanted. The 

 above specimens are all from Eureka, Utah. A single specimen, Mus. 

 No. M 9419, from Mammoth, Utah, exhibits crystals differing some- 

 what in habit from any of the above. This habit is shown in Fig. 6, 

 PI. LI, and is characterized by prominent development of the basal 

 planes, and elongation in the direction of the macro-axis, producing a 

 tabular form. A brachydome not previously noted on olivenite also 

 occurs on these crystals. This lies between the base c (001) and the 

 unit dome e (on) and its determination is based upon its occurrence 

 in the zone noted and the measurement e /\ s = 7 50'. Occur- 

 ring with crystals of this habit are others of the habit shown in Fig. 

 2, PI. LII. All the crystals on this specimen, Mus. No. M 9419, are 

 greenish-black in color, opaque, and have brilliant planes. They 

 occur encrusting cavities in massive malachite. 



In the measurement of the crystals as a whole it was found that 

 the angles observed did not agree with those obtained from the axial 

 ratios of Washington as fully as could be desired. This discrepancy 

 was especially noticeable in the measurement of the prism m a m"' . 

 A large number of measurements of this angle gave a value closely 

 approximating 87 28', which differs nearly a degree from that 

 obtained by Washington, his value being 86° 26'. Further, the 

 measurement obtained for e a e' , approximated in several good 

 measurements closely to the value 69 18'. These values agree more 

 closely with the measurements of Phillips * than with those of Washing- 

 ton. The excellence of the measurements on the Eureka crystals 

 seemed to warrant the calculation of axial ratios from them, and these 



♦Mineralogy, 1823, p. 319 



