Penfield and Sjperry — Mineralogical Notes. 329 



any simple compound, while the supposition which we have 

 made gives ratios which are very simple and exact. 



8. A very pure magnesia mica, phlogopite, from Edwards, 

 St. Lawrence Co., N. IT. 



Our attention was first called to this mineral by Mr. C. D. 

 Nims of Philadelphia, N". Y., who had obtained it from the 

 talc mines in Edwards. Later one of us,* while making a 

 mineralogical excursion in St. Lawrence Co. under the auspices 

 of the U. S. Geological Survey during the summer of 188T, 

 visited the locality and was generously supplied with material 

 by Mr. T. J. Hooper, superintendent of the Anthony Mine of 

 the Adirondack Pulp Co. 



The mineral occurs filling a narrow seam or vein associated 

 with tremolite and the pure white talc which is extensively 

 mined in that region. It occurs in large plates, without regular 

 crystalline outline except an occasional hexagonal marking, 

 which are more or less bent and intergrown. The cleavage is 

 not quite as good as in most micas, being more like that of 

 ripidolite ; the folia are elastic when very thin but thicker 

 folia, over 0*l mm , crack and break quite readily in three direc- 

 tions parallel to the fracture figure. Thin plates of the mica 

 appear perfectly clear and colorless ; plates 2 mm thick and over 

 have a very delicate sea-green color, thick pieces being exceed- 

 ingly light colored and transparent, for a mica, in the direction 

 of the vertical axis. The six-rayed fracture figure (Schlag- 

 figur, German) and the pressure figure with rays at right 

 angles to it are obtained by driving a steel point into the plates 

 or pressing with a steel rod with rounded end against thin 

 plates on an elastic support. The optical properties are not 

 constant, even in the same plate. In convergent polarized 

 light many pieces give a uniaxial interference figure, but 

 usually the dark cross opens into hyperbolae always showing a 

 small optic axial angle ; this was not measured because it was 

 so variable. The plane of the optic axes is the plane of 

 symmetry, parallel to one of the rays of the fracture figure, 

 making it a mica of the second kind. The double refraction 

 is negative. 



Before the chemical analysis or any tests were made the 

 nature of this mineral was questionable, such minerals as 

 brucite, a highly crystallized variety of talc or a light colored 

 ripidolite, suggested themselves rather than mica. 



The specific gravity of the mineral was taken very carefully 

 on the chemical balance, after boiling, to expel any air from 

 between the folia, giving 2*793 and 2 791. The following 

 analysis is by Mr. Sperry : 



* Penfield. 



