60 MINERALOGY AND LITHOLOGV. 



42. Spodumene [3 Li^ Si 0=^ + 4 AP Si^ 0=*]. 



This is another silicate isomorphous with pyroxene. It is found in 

 good crystals at Winchester. Its crystals are white in color, and usually 

 flattened by the wide development of the orthopinnacoid. The ingredi- 

 ent that characterizes this mineral is its lithia. The crystals resemble 

 those from Huntington, Mass., which Prof. Brush found to contain more 

 than five per cent, of that oxide. The mineral is easily recognized by 

 its large, tabular crystals, its easy cleavage parallel to the orthopinnacoid, 

 and the carmine color that it imparts to the blow-pipe flame. 



43. Anthophyllite [(Mg, Fe) Si O3]. 



This mineral occurs in a talcose rock at Richmond. It is character- 

 ized by its fibrous structure, its brown color, and its infusibility before 

 the blow-pipe. It is the orthorhombic species of the hornblende group, 

 and hence may be distinguished in a thin section by the circumstance 

 that it is dark between crossed Nicol prisms when its fibres are parallel 

 to the plane of vibration of the light; but it has no significance in our 

 petrography, although Brooks has found it as a common constituent of 

 rocks about Lake Superior, which occur in formations lithologically 

 related to some of ours. 



44. Ampiiibole [R Si O3]. 



R standing usually for Ca Mg and Fe. It also often contains alumina 

 and alkali. 



Amphibole here, as elsewhere, is one of the commonest minerals. 

 Fine crystalline specimens are found. It is a very common ingredient 

 of the rocks, and forms rock masses by itself. 



The common dark colored variety, which is usually called hornblende, 

 has been found abundantly in superb crystals at the Franconia mines in 

 Lisbon. Long-bladed crystals are also found there, and at Warren. 

 Hornblende is found in fine crystals at Exeter, Hanover, Winnipiseogee 

 lake (on Red hill), and Moultonborough. 



Actinolite is the lighter green variety that usually occurs in smaller, 

 longer crystals. It is found at Unity and Lisbon, and is common in 

 unremarkable occurrences. 



