474 PALACHE AND schaller: hodgkinsonite 



tion and in one operation from tables of the Descending Expo- 

 nential/ the operation of calculating a series of values from the 

 exponential equation involves less labor than from a cubic equa- 

 tion. (3) Altho extrapolation is, in general, an operation beset 

 with many pitfalls, nevertheless, if an extrapolation is unavoid- 

 able, it is more reasonable to employ a function of proper general 

 form than to take some random function which can not be ex- 

 pected to fit the experimental results except over a small part 

 of the range of observation. 



MINERALOGY. — Hodgkinsonite, a new mineral from Franklin 

 Furnace, N. J. C. Palache, Harvard University, and W. T. 

 Schaller, Geological Survey. 



The mineral here described was sent to the Harvard Miner- 

 alogical Museum for identification in April of this year by Mr. 

 J. J. McGovern of Franklin Furnace, New Jersey. On being 

 informed that the mineral was of a new species, material for 

 further study and for analysis was freely supplied by Mr. H. H. 

 Hodgkinson, M. E., Assistant Underground Superintendent of 

 the mine, who first found the mineral in the mine workings and 

 whose name it bears. Mr. Hodgkinson states that the new min- 

 eral was found in the northern part of the ore body, in that part 

 of the Parker Mine formerly known as the Hamburg Mine and 

 quite near the hanging wall of the west leg of the ore body, be- 

 tween the 850- and 900-foot levels. The locality was marked 

 by a number of slips and faults, along some of which the mineral 

 occurs. It has been found in a number of specimens during the 

 year but nowhere in abundance. 



Hodgkinsonite is a hydrous silicate of zinc and manganese 

 ■crystallizing in the monoclinic system. It occurs in seams in 

 massive granular ore of the typical willemite-franklinite mixture; 

 the seams are generally very thin with but a film of the mineral 

 which is always associated with white barite and not uncommonly 

 with plates of native copper. Locally the film thickens to a 

 narrow vein and then the new mineral may show individuals up 

 to 2 cm. across, sharply angular in form and apparently with 



^ Such, for example, as those in Becker and Van Ostrand's hyperbolic functions 

 (Smithsonian Mathematical Tables, Washington. 1909). 



