670 WELLS AND LARSENI LORETTOITE 



are about half a millimeter in width. The specific gravity of 

 the Loretto specimen, as determined by the picnometer method, 

 is 7.39; that of the University of California specimen, as deter- 

 mined with a Joly balance, is 7.65. The cloudiness of the Loretto 

 specimen is due to minute gas cavities which may account for the 

 apparently low specific gravity. The Loretto specimen fuses 

 readily in the flame of a candle (F = 1) to a mass which on cool- 

 ing is a yellow, crystalline bead. It has a hardness of about 3. 

 Its luster is adamantine, its color honey-yellow, and its streak 

 pure yellow. 2 It is optically negative, sensibly uniaxial, and the 

 optic axis is normal to the cleavage. The indices of refraction 

 as measured in sulphur-selenium melts are, for the Loretto 

 specimen : 



Wu = 2.40 ± . 02 

 e Li = 2.37 ±0.02 



and for the specimen at the University of California : 



WLi = 2.35 =•= 0.02 

 €Li = 2.33 ± 0.02 



The specimen from the University of California is less clouded 

 than that from Loretto, and basal sections show a delicate cross- 

 grating at 90° due to the minute gas inclusions collected along 

 certain planes. The mineral is therefore probably tetragonal 

 with very perfect basal cleavage. 



Chemical properties. Lorettoite dissolves easily in hot dilute 

 nitric acid, leaving only a very slight residue. It dissolves 

 slowly in hot dilute hydrochloric acid, and lead chloride sepa- 

 rates from the solution on cooling. Sulfuric acid decomposes it 

 very slowly. It is not appreciably soluble in hot water. The 

 slight effervescence of the Loretto specimen with acids is due 

 to a small amount of carbonate. 



A microscopic examination of the powder analyzed showed a 

 little impurity, estimated at 2 per cent, consisting chiefly of 

 carbonate and a little of an opaque mineral, lead gray in reflected 



2 Following Ridgway's Color Standards and Nomenclature, 1912, the color is 

 honey-yellow (19" — ), and the streak strontium-yellow (23' — ). 



