1ST3.] °^^ [Genth.- 



2G. Chloritoid. 

 This mineral has been observed at many of the corundum localities. 

 It is associated with diaspore, mica and cyanite as Kassoibrod in the 

 Ural ; in Asia Minor with corundum, diaspore and margarite ; at Chester, 

 Massachusetts, with emery and diaspore. One specimen from Augusta 

 County, Virginia, consists of chloritoid, damourite and grains of corun- 

 dum ; I found one little crystal in the washings of the soil from the Cul- 

 sagee Mine. A very interesting occurrence is that in the pyrophyllite 

 slates of Chatham County, Xorth Carolina, where it occurs in minute 

 shining scales of a dark blackish-green color disseminated through the 

 white rock. With great difficulty I have selected a quantity of appa- 

 rently pure material for analysis. 



Sp. Gr. = 3.353. 

 SiO, 26.13 contains oxygen = 13.94 



FeO 23.01 5.11^ 



MnO trace. V 5.49 



MgO 0.94 0.38) 



Ignition G.91 6.14 



A1,0 3 40.11 18.69 



Fe,0 3 3.44 



100.54 

 The oxygen ratio of RO : R,0 3 = Si0 2 : H,0 is = 0.83 : 3 : 2.12 

 : 0.97 = 4 : 15 : 10 : 4, giving the formula : 4 RO, SiO, + 5 R ,< > :; , 

 4 SiO, + 4 H,0, which corresponds closer to my analysis than the formula 

 4 RO, SiO, — 4 R,0 3 , 3 SiO,, which is generally given. However, there 

 may have been a minute quantity of pyrophyllite in my material which 

 might be the cause of this discrepancy. 



27. Margarite. 



This species had been known for a long time from one locality, Sterzing 

 in Tyrol, but not until the almost simultaneous discovery of it in association 

 with the corundum from Pennsylvania and North Carolina, by B. Silliman 

 and with emery in Asia Minor and Greece by J. L. Smith, its importance 

 became apparent. Since then it has been observed almost everywhere 

 with corundum, but a great portion of the laminated varieties of damour- 

 ite have been confounded with it ; it so much resembles the latter in all 

 its varieties, that the only safe way for distinction is by chemical analy- 

 sis. 



At Unionville, many of the corundum crystals have a coating of a soft 

 mineral, and sometimes the whole mass of the crystals is converted into 

 it ; a qualitative analysis proved these coatings to be margarite. More 

 fully investigated were the following varieties : 



a. A part of a crystal, showing the basal plane o, and a pyramid, 

 which seems to be §2 and consisting of a grayish- white soft mineral. To 

 the naked eye it looks like an amorphous substance without lustre. 



