F. A Genth — Contributions to Mineralogy. 4'.* 



1. _• 3. 



Spec Grav 3-154 3151 



Loss by ignition 1*80 M»7 2*42 



SiO 36*98 36-86 36*22 



Al.O, ) 1 mm. 60-76 



I O, ... \ M °° 0-7J 0-88 



MgO o-io 



Corundum 1*12 trace trace 



100-56 100-05 100*28 



VyaniU and Rhmtizite. — Both tlie typical blue, bladed 

 cyanite and the so-called rbcetizite occur pseudomorphous after 

 andalusite, some of the specimens indicating that the latter lias 

 occurred in stout crystals, the largest from 70 to 80" ,m in size. 



The blades of the cyanite are of a bluish white to sky-blue 

 color and often from 10 to 25 nun broad, in many specimens, 

 however, much smaller, sometimes radiating and gradually 

 becoming masses of interwoven fibers. Associated are small 

 quantities of quartz and mnscovite which latter especially lines 

 the cavities. Blue corundum in small grains is disseminated 

 through the mass. 



The rhietizite of a grayish brown color and a more or less 

 fibrous Btrnctnre is the more frequent form of alteration of the 

 andalusite, and, in breaking the masses, many show in the 

 interior the prismatic forms of the original andalusite. It 

 is often intermixed with a large quantity of grains of blue 

 corundum, muscovite and rarely of chloritoid. 



Muscovite. — There is hardly a specimen of the andalusite, 

 rluptizite and cyanite in which muscovite could not be ob- 

 served as a direct alteration of these minerals. In the rhaeti- 

 zite it is frequently found in somewhat larger quantity and, 

 together with chloritoid, often with a nucleus of blue corun- 

 dum. This muscovite has a brownish white color. A partial 

 analysis of it gave : 



Loss by ignition .. _ 6'49 



Na o 0-87 



Kfi . 9*28 



Margarite i in part). — No crystallized variety of margarite 

 has been found, but some of the andalusite, still retaining the 

 original form, has been altered into a soft, fine-grained, or com- 

 pact mineral, in some portions discolored by ferric hydrate, and 

 mixed with some fine scales which are probably muscovite. 

 After purification with dilute hydrochloric acid, it was ana- 

 lyzed by Mr. Jas. S. de Benneville (a) and me (h) with the 

 following results : 



Am. Jour. Sci.— Third Series, Vol. XXXIX. No. Ti\).— Jan., 1890. 

 4 



