S. L. Penfield — Crystallization of Herderite. 337 



just described, but they are not so perfect and they do not 

 show the reentrant angle. 



Herderite from Greenwood, Maine. 



In this township herderite has been found at two localities. 

 At one of these it is a hydro-herderite and, as represented by 

 a small specimen in the Brush collection and by several crys- 

 tals belonging to Mr. Geo. L. Noyes of Norway, Me., it occurs 

 in crystals measuring 15 mra in diameter, but poorly developed 

 and presenting no forms that could be accurately measured on 

 the reflecting goniometer ; with the contact goniometer, how- 

 ever, the following were identified : b, 010 ; c, 001 ; t, 032 and 

 g, 364, f-2. The development of the forms is shown in fig. 11, 

 j having been observed only on crystals from this locality. 



At the second locality it is a hydro-fluor-herderite and is rep- 

 resented only by a single specimen belonging to Mr. Noyes. 

 This shows several herderites attached to a large quartz crystal. 

 The largest herderite measured parallel to the axial diame- 

 ters a, 9 mm ; b, 5 mm and c, 3^ mm and had trfe habit shown in fig. 

 12. The crystals were not well adapted for measurement with 

 the reflecting goniometer and they were not detached from 

 the quartz, but the forms were identified by approximate 

 measurements made from wax impressions of the faces. The 

 following were observed : b, 010 ; m, 110 ; I, 120 ; e, 302 ; u, 

 011 ; n, 331 ; n, 331 ; q, 332 ; r, 121, 2-2 and p, 391, 9-3. The 

 last two have been observed only on the crystals from this 

 locality. The forms q, r and p round into one another and in 

 this respect the crystals resemble those from Paris, where the 

 positive hemi-pyramids are curved and indistinct. 



Herderite from JEhrenfriedersdorf Saxony. 



The material from this locality is extremely rare and the 

 author has had no opportunity of examining it. It is un- 

 doubtedly monoclinic and the orthorhombic habit described by 

 Haiclinger is the result of twinning. In the description given 

 by Des Cioizeaux* of the optical properties it is very evident 

 that he was dealing with a twin crystal as he states that about 

 the acute bisectrix three sets of ring systems were observed. 

 The following values for 2E are given 124° 35', 123° 10' and 

 122° 24'. From the axial ratio given on page 33 L it would 

 be expected that the composition of the mineral is interme- 

 diate between that of the Stoneham and Paris herderite. 



Conclusions. — As has been shown, herderite is a mineral of 

 variable composition and it seems best to designate the dif- 



*Loc. cit. 



