84 NEW YORK STATE MUSEUM 



Calcite. Commonly called " calc-spar." Crystals show many 

 variations, though all have a threefold development such as three- 

 sided prisms, pyramids or rhombohedrons. Very perfect cleavage 

 in three directions yielding fragments with faces which meet at 105° 

 and 75°. Color, white when pure. Relatively soft, can be scratched 

 with a copper coin. Composition, carbonate of lime. 



Calcite is the chief constituent of the Grenville limestone, generally 

 making 75 to 95 per cent of the mass and is therefore very abund- 

 ant in the Adirondacks. 



Chalcopyrite. Commonly called " copper pyrites." Rarely in 

 crystals. No cleavage. Color, deep brass-yellow. Relatively soft, 

 can be scratched by a copper coin. Composition, sulphide of copper 

 and iron. 



Fairly widespread as a very minor constituent of the anortho- 

 site and often clearly visible to the naked eye. 



Coccolite. See pyroxene. 



Feldspar. There are several important varieties of feldspar with 

 certain features in common as follows : two well-defined cleavages 

 at or near 90°; scratched by quartz or flint but not by a knife; 

 crystals in prismatic forms usually making angles of 120° ; compo- 

 sition, silicate of aluminum with potash, soda or lime. Color, white, 

 pink, or greenish gray. Orthoclase is a white to pinkish potash feld- 

 spar with two cleavages at exactly 90°. Microcline is much like 

 orthoclase except for cleavages at 89° 30' and crossed striations 

 when viewed as a thin slice under the microscope. Alhite is a white 

 soda feldspar with cleavages at 86° 24'. Oligoclase is a greenish 

 white soda-lime feldspar with cleavages at 86° 32'. Labradorite is 

 a greenish gray to dark gray lime-soda feldspar with cleavages at 

 86° 4", and it sometimes exhibits a play of colors on one cleavage 

 face. Anorthite is a white lime feldspar with cleavages at 85° 50'. 

 Plagioclase includes albite, oligoclase, labradorite and anorthite. and 

 these nearly always exhibit well-defined striations on one of the 

 cleavage faces. 



Orthoclase is a very prominent constituent of the syenite-granite 

 series and pegmatite, but is rare in the other igneous rocks. It is 

 common in many of the Grenville gneisses. Albite and anorthite 

 seem to be uncommon in the Adirondacks. Microcline and oligo- 

 clase in smaller amounts generally accompany orthoclase. Labra- 

 dorite is the chief constituent of the anorthosite, gabbro and dia- 

 base. It also occurs in some of the Grenville gneisses. 



Garnet. Exists in several varieties differing in color and com- 

 position. Most common in the Adirondacks is alnianditc garnet 



