Genth.] '384 [Sep . 19 . 



part of France, the dillnite with the diaspore of Schemnitz, and others, 

 of which the species has not heen sufficiently identified ; they are mostly 

 amorphous and their relation to the corundum is not striking enough to 

 dwell more fully upon them. I turn my attention now to 



1G. Damourite. 



This species has heen estahlished on a mica-like mineral, an aggregate 

 of fine scales, forming the gangue of cyanite at Pontivy, Brittany. It 

 will be seen in the sequel that it is one of the most important products 

 of alteration of corundum, from which it is either directly formed, or in- 

 directly, after the corundum has first been changed into cyanite or fibro. 

 lite, which latter are subsequently converted into damourite. There is 

 hardly a species, which assumes so many different shapes as this, and it 

 is often impossible to determine it without analysis. S. P. Sharpless* 

 was the first to prove that mica- like crystals, which accompany the dia- 

 spore from near Unionville, Newlin Township, Chester County, Pennsyl- 

 vania, which always had been mistaken for margarite (emerylite) were 

 damourite. 



At Unionville, damourite is found in the following forms : 



a. In crystals frequently having the lateral and sometimes the basal 

 planes well developed ; they appear to be hexagonal plates, but are 

 prob.ibly rhombic. They are sometimes radiating and fan-shaped, and 

 the crystalline plates from one to three inches in diameter. Their color 

 is generally white to greenish-yellowish and brownish-white, but when 

 treated with chlorhydric acid, which removes a little ferric hydrate which 

 colors them, they are white with a very delicate shade of sea green- 

 rarely as deep as grass-green. Their lustre is pearly, sometimes inclin- 

 ing to vitreous. 



These crystals or crystalline plates of larger or smaller size are directly 

 attached to the granular grayish or brownish-white corundum or in the 

 mass of the same ; occasionally there is between them and the corundum 

 a small seam of a crystallized dark-green chloritic mineral. Black tour- 

 maline is another not uncommon associate, and especially, where the rare 

 mineral diaspore appears, slender crystals of dark blueish, or brownish, 

 green tourmaline are met with.- This is the variety analyzed by S. P. 

 Sharpless and Dr. G. A. Koenig (a). 



b. Another variety of damourite consists of an aggregation of grayish 

 and yellowish-white scales of one-sixteenth to not over one-quarter in- 

 ches in diameter. After cleaning them with dilute chlorhydric acid they 

 are silver-gray. They form a coating upon and sometimes occupy the 

 whole of former corundum crystals and their aggregations are real 

 pseudomorphs after corundum, generally with a core of original mineral. 

 Dr. Isaac Lea has a fragment of a beautiful crystal of blue corundum 

 over three inches in length and about two and a-half inches in diameter, 

 which is coated with a coust of scaly damourite from one-eighth to one 



*S. P. Sharpless, Sill. Journ. [2] XLVII.319. 



