£. K. Emerson — Mineralogical Notes. 233 



Art. XXIV. — Mineralogical Notes ; by B. K. Emerson. 



1. Limonite pseudomorph after cliaba7itite, after anhydrite. 



Years ago I discovered anhydrite in large bluish-white 

 masses in the trap at Larrabee's Quarry on the north line of 

 Holyoke.* It is in tabular aggregates resembling cleaveland- 

 ite, slightly radiate, but sometimes radiating so rapidly that 

 plates bend 90 degrees in one inch. The plates vary from one- 

 eighth inch thick to extreme thinness. It shows three perfect 

 cleavages, and striated crystal faces. Pyrite and calcite are in 

 the same cavities suggesting its origin. In many cases regular 

 prismatic and tabular cavities occur in the zeolite-calcite aggre- 

 gates in the cavities of the trap, which I have been accustomed 

 to refer with doubt to selenite.f Recently I have received 

 specimens from the third Westfield quarry, counting from the 

 south, on hillock 380 feet above sea, and 1/2 mile north of the 

 railroad, which show such cavities reaching 2 inches in length 

 and width and 1/4 inch in thickness, but generally much 

 thinner down to 1/32 of an inch. In several cases the enclos- 

 ing mineral has penetrated the two perfect cleavages of the 

 original mineral which are rectangular ; the one parallel to the 

 broadest surface, c, and the other at right angles thereto and 

 parallel to the greatest length of the crystal, b. At times the 

 exterior of this broadest face is preserved in a perfect cast 

 which is striated like the b face of anhydrite and at other times 

 it has been etched during enclosure so that the tracing of the 

 two rectangular perfect cleavages parallel to b and c are well 

 shown on a. The crystals were flat rectangular plates some- 

 times cut by a brachydome. 



These cavities have been filled by diabantite which appears 

 first in small tufts and then fills the space entirely, showing a 

 central suture where the two growths have come together. 

 These tufts are often altered to bright gold-yellow forms 

 "which I have described as diabantite- vermiculite,^ and the com- 

 plete fillings also show every stage of the change from fine 

 fibrous green diabantite to a porous impure limonite, which 

 latter is thus a pseudomorph by replacement of anhydrite, and 

 by chemical alteration of diabantite. 



The same negative forms have been found at the Cheapside 

 quarry south of Greenfield in thinnest plates and in long stout 

 prisms coated with datolite, or enclosed in the same. The 

 blades are often over three inches long. The blades have also 

 been inclosed in quartz and sometimes several quartz crystals 



* Mineral Lex. Old Hampshire Co., Bull. 126, U. S. G. S., p. 26, 1896. 

 + Loc. eit., p. 90. % This Journal, xxiv, 198, 1882. 



