﻿314 E. S. Dana — Brookite from Magnet Gove, Ark. 



Art. XXXYII. — On the Brookite from Magnet Gove, Arkansas ; 

 by Edward S. Dana. With Plates VIII and IX. 



The species brookite is interesting, among other respects, be- 

 cause of the great variety of form exhibited by the crystals from 

 the different localities at which it occurs. This fact is well 

 exhibited in the figures on Plate XXXIX, of Schrauf's Atlas. 

 In this regard the crystals from Magnet Cove, Arkansas, are 

 especially remarkable, for though the number of planes ob- 

 served on them is not large, the variation in habit is most un- 

 usual for crystals from a single locality. 



The brookite from Magnet Cove was first mentioned by 

 Shepard* in 1846, who supposed it to be a new species and 

 gave to it the name arkansite. In 1876 vom Eathf gave an 

 interesting account of the paramorphs of rutile after brookite, 

 which are not rare at this localitj? - , and also figured several of 

 the common forms. A few months since S. L. Penfield^: pub- 

 lished a paper upon the arkansite in which he gave figures of 

 four forms, and also the results of measurements of a crystal of 

 unusual perfection. It might seem perhaps as if these papers 

 had exhausted the interest of the subject ; and this may be 

 true so far as the commonly occurring types of forms are con- 

 cerned. Through the kindness of Mr. Clarence S. Bement of 

 Philadelphia, the writer has had the opportunity of studying his 

 large series of crystals of this species, and the variety among 

 them has been found to be so great that they have seemed 

 worthy of special description, with also some fullness of illustra- 

 tion. These crystals have been selected from time to time with 

 great care from a large amount of material, and they represent 

 the best specimens which the locality has afforded. Most of 

 the crystals are isolated, the arkansite occurring chiefly in 

 loose crystals scattered through the soil. 



The planes which have been determined on these crystals are 

 as follows : 



Pinacoids, a (100, i-i), c (001, 0)\ prisms, ? (210, »-2), m (110, I), <J> (120, «-2), 

 new; brachydome. < (021, 2-2); pyramids, z (112, $\ * (124, £-2), #(234, f-f), 

 e(122, 1-2). 



The crystals may be roughly divided into those of prismatic, 

 and others of pyramidal habit. In the former, figures 1 to 12, 

 with also figs. 14, 15, 16, 18, (Plates VIII, IX), the fundamen- 

 tal prism, m, usually predominates ; the forms vary much, how- 

 ever, according to the pyramid by w*hich they are terminated. 

 Figure 1 is a common form, occurring in crystals of relatively 



* Am. Journ. Sc, II, ii, 250, 1846. f p ogg- Ann., clviii, 40V, 1876. 



% Am. Jour. Sc., III, xxxi, 387, 1886. 



