442 NATURAL HISTORY. 



quently colored brilliantly green, blue, red. When 

 heated, exhibits a greenish, but vivid, phosphorescence. 

 H. = 4.0. G. = 3.1 to 3.2. Ranks on account of its 

 clearness and bright colors among the handsomest of the 

 minerals, and is very common in all the mining districts 

 of Germany, particularly in those of the Hartz and 

 Black Forest. It has the peculiarity of mixing readily 

 with other metallic substances ; as it fuses easily, is used 

 as a flux to aid in reducing copper and other oi'es, whence 

 its name Fluor. Fluor spar, in combination with sul- 

 phuric acid, developes fluoric acid, which is employed in 

 etching on glass. The more beautiful crystal specimens 

 are occasionally employed by the lapidary in making 

 ornaments for inlaying cabinets, etc. ' 



III. Hornblende Tabular Spar seldom occurs 

 crystallized, mostly firm or compact ; luster vitreous, - 

 inclining to pearly. Slightly translucent on the edges ; 

 colorless or colored, yellow, gray, red, or brownish-Avhite; 

 fracture uneven ; brittle : when fiibbed or heated, phos- 

 phorescent. Occurs in granular limestone ; abounds in 

 Hungary, also in the United States, and is an essen- 

 tial constituent of certain rocks, as syenite, trap rock, 

 and hornblende slate. H. = 4.5 to 5.0. G. = 2.8 

 to 2.9. 



Common Hornblende. Mostly in the form of crystals, 

 but also massive and slaty cleavage ; face granulate or 

 disseminate and radiate ; translucent on the edges : crow- 

 black, dark, or blue-black green ; is the principal consti- 

 tuent of greenstone. Found extensively in the primary 

 and sedimentary rock formations, associated with the 

 metallic ores. Abounds in the BLick Forest and Tyrol ; 

 equally so in the mining districts of the United States. 

 H. = 5.0 to 6.0. G. = 2.9 to 3.4. 



