280 Merrill and Packard — Azure-blue Pyroxenic Pock. 



row, nearly vertical bed, enclosed between granitic and basic 

 eruptives, forms a continuation of the peculiar banded ser- 

 pentinous rock commercially known as ricolite and which has 

 been put upon the market as an ornamental stone. 



Under the microscope, in thin sections, the rock is seen to 

 consist wholly of short and stout colorless granular pyroxenes 

 interspersed with occasional small areas of interstitial calcite. 

 None of the pyroxenes show idiomorphic forms but the 

 structure is eminently granular, the individual crystals varying 

 in size up to 1 mm. in greatest length. Cleavage is very 

 poorly developed, but an occasional basal section shows a 

 nearly rectangular parting and gives a biaxial interference 

 figure with the optic axis lying in the plane of symmetry. 

 The blue color so striking in the hand specimens is naturally 

 quite lacking in the section, nor is there evident pleochroism. 

 As is often the case with rocks of this class a serpentinous 

 alteration has set in giving rise to a beautiful compact oil-yel- 

 low and greenish serpentine with the liberation of abundant 

 free calcite, but so far as observed no chalcedonic or other 

 form of free silica. The absence of secondary silica in altera- 

 tions of this kind, has been noted by Mr. Merrill in previous 

 papers,* as in marked contrast with serpentines resulting from 

 the alteration of rocks of the peridotite group which are 

 nearly always traversed by strings and veins of chalcedony. 



A piece of the blue rock free from serpentine was pulver- 

 ized, treated with warm hydrochloric acid to remove calcite 

 and then boiled in an alkaline carbonate. The analysis gave : 



Molecular ratio. 



SiO„ 54-30 -905 



MgO_. 18*33 -458 



FeO I'll -015 



CaO.. 25-00 -446 



98-74 



This reduces to the formula, CaMgSi 2 6 , which is that of 

 malacolite. 



The striking blue color of the mineral would appear to be 

 due wholly to iron protoxide as careful tests fail to indicate 

 the presence of other metallic substances nor is the color 

 changed by the action of strong acids or moderate heat. 



National Museum, Feb., 1892. 



* On the Serpentine of Montville, New Jersey. Proc. United States National 

 Museum, 1888, p. 105: Notes on the Serpentinous Rocks of Essex Co., New York, 

 etc., ibid, vol. xii, 1889, p. 595; and On the Ophiolite of Thurman, Warren Co., 

 New York, this Journal, vol. xxxvii, March, 1889, p. 189. 



